Quality of life instruments and definitions in individuals with spinal cord injury: A systematic review

Abstract

Study Design

A systematic review.

Objective

To critically review quality of life (QOL) instruments used with spinal cord injury (SCI) populations.

Setting

Vancouver, Canada

Methods

A systematic literature review was conducted for publications assessing the measurement properties of QOL outcome measures. Pre-established criteria were used to evaluate the measurement properties.

Results

Fourteen articles reporting on 13 QOL instruments met the inclusion criteria, including the PRISM, QWB, Qualiveen, SIP68, SF-36, SF-36V, SF-12, SF-6D, QLI, QOLP-PD, SWLS, SWBI, and the WHOQOL-BREF. The SF-36 and WHOQOL-BREF have been widely used and validated. The SIP68, QOLP-PD, SF-36V and SWBI are promising with limited investigation. The Qualiveen and PRISM performed well, and are specific to SCI complications.

Conclusion

The WHOQOL-BREF, is presently the most acceptable and established instrument to assess quality of life after spinal cord injury. The SIP68, QOLP-PD, SF-36V and SWBI are promising, however, require further evaluation of their measurement properties..

Introduction

Attaining an acceptable quality of life is considered by many to be the ultimate goal of rehabilitation following spinal cord injury (SCI).^(1–2) During the past few decades advances in medical care are enabling persons with SCI to survive the initial injury and to prolong their life expectancy post-SCI.⁽³⁾ The need for outcome measures assessing health and quality of life (QOL) following rehabilitation is therefore becoming increasingly important.^(4–9) It is clear that simple outcomes assessing function are insufficient in measuring rehabilitation after SCI,^(7,9) and in capturing the adaptation of perceptions and values in patients after SCI.^(7,9) In fact, it has been suggested that high levels of QOL is synonymous with positive rehabilitation outcomes, and many agree that QOL should be measured in tandem with traditional outcomes assessing functional rehabilitation. ^(9,10) Such measurements provide different yet complimentary information that aid clinicians in their efforts to help those with SCI. Although an altered life is an inevitable outcome of SCI, literature shows that QOL after SCI is not uniformly worse, but rather a spectrum of recovery outcomes exist, that range from QOL well below the general population, to QOL that surpasses healthy population averages.⁽⁹⁾

QOL is a difficult construct to capture. Description of what constitutes the quality of someone’s life is an important factor in our ability to assess, measure, and improve treatment outcomes and post-injury lifestyles. A clear definition of QOL has yet to emerge, which is due in part to a lack of consensus on a general definition of QOL.⁽¹¹⁾ As such, our ability to accurately measure QOL among populations is limited. This is especially true with SCI populations.

Dijkers⁽¹²⁾ proposed a scheme for classifying QOL instruments whereby they are conceptualized from the perspective of an outsider, an ‘objective’ view, or an insider, a ‘subjective’ view. All QOL instruments include reactions to or evaluations of the characteristics of a person’s life (achievements) in the context of their expectations about those achievements, either implicitly or explicitly.⁽¹²⁾ Therefore, the distinction whether the instrument is based on an ‘objective’ or ‘subjective’ view, is determined by: 1) whose expectations and evaluations are used; and 2) which of the three (reactions/evaluations, achievements, expectations) are made explicit.

The objective approach to assessing QOL evaluates characteristics that can be impartially measured by an external appraiser.⁽¹²⁾ These types of instruments assume: 1) that all individuals have the same domains that are important in their lives or same goals; and 2) happiness or satisfaction in life is directly proportional to the degree to which an individual achieves these standards or goals.⁽¹²⁾ Most instruments assessing health status (also known as health-related QOL, HRQOL), as well as utility measures are considered to be objective approaches.⁽¹²⁾ These types of instruments, however, are limited as they tend to overestimate the impact of health and underestimate the other non medical aspects such as the individual’s values and preferences. ^(13,14)

The subjective approach to measuring QOL assumes that QOL can only be determined by the individual.⁽¹²⁾ Instruments developed using this approach consider an individual’s emotions or feelings (happiness/affect) or evaluation (life satisfaction) in the context of their expectations and achievements.⁽¹²⁾ Life satisfaction can be further differentiated into satisfaction with overall QOL and satisfaction in specific domains (e.g. job relationships, health, etc.) comprising QOL.⁽¹⁵⁾

As improved QOL, be it subjective or objective, is indicative of the success of treatment programs or progress in the life of a SCI patient,^(9,16) it should be routinely measured among SCI patients. Our purpose in this review, therefore, is to classify QOL instruments in use among SCI population as either objective or subjective, present evidence from the literature on the measurement properties of various QOL measures, and evaluate the properties against pre-established criteria. Such classification and evaluation will assist both clinicians and researchers select QOL measures appropriate to the context of their rehabilitation programs or research studies.

Methods

Search Strategy

A review of the QOL literature from 1986 to April 2009 was conducted. Primary data sources included the Pubmed, CINAHL, Embase, Medline, HaPI, Psycinfo, and Sportdiscus electronic databases.

The key word spinal cord injury and its related terms, paraplegia, quadriplegia, or tetraplegia, were used in conjunction with the terms, validity, reliability, or responsiveness. To complete the search, these terms were then combined with the names and abbreviations of instruments used to assess the QOL in individuals, including the names of all measures which met the criteria. After deleting non-relevant and duplicate papers, titles, key words and objectives were examined by two investigators, and papers that did not specifically assess measurement properties of the outcome measures listed above with an intent to validate their utility, and papers with populations not entirely SCI were eliminated. Eligibility and the measurement properties of the instruments were evaluated by three team members.

Inclusion Criteria

To be included in this review, the instruments had to satisfy several requirements, which included: 1) the primary purpose of the paper was to evaluate the measurement properties of a QOL instrument, i.e., Level one papers based on the classification of Kalpakjian et al.⁽¹⁷⁾; 2) the sample included an SCI population, 18 years of age and older; 3) the data specific to SCI were reported; 4) the paper was published in a peer-reviewed journal; and 5) the paper was written in English.

Classifying the Instruments

Instruments were classified as either primarily objective or subjective QOL measures as per Dijkers ⁽¹²⁾ guidelines. Most authors clearly distinguish their instrument or definition of QOL as objective^{(5,16,18–20)} or subjective.^{(1,6,9,20,21)} Where no distinction was specified, instruments were classified according to the authors’ definition of QOL,⁽⁷⁾ and/or the item content and scoring model.^(22,23) For example, instruments addressing HRQOL or the presence, severity, and impact of specific health factors relating to QOL were considered objective, and instruments measuring life satisfaction, or using scoring relationships between satisfaction and importance were classified as subjective.

Evaluation Criteria

Criteria for assessing the instruments’ measurement properties are based on the Outcome Measures chapter in the Spinal Cord Injury Rehabilitation Evidence (SCIRE)⁽²⁴⁾ systematic review, which are adapted from the Desirable Characteristics of Outcomes Research Measures for with People with Disabilities defined by Andresen et al.⁽²⁵⁾ Table 1 provides a description of the evaluation criteria.

Table 1.

Criteria for Instrument Evaluation

Criteria	Description	Evaluation
Reliability	Degree to which an instrument is consistent or free from random error	Test re-test repeatability (ICC and kappa) A = >0.75 B = >0.40, <0.75 C = <0.40
		Internal consistency (Coefficient Alpha)  A = >0.80  B = <0.80, >0.70  C = <0.70
Validity	Degree to which an instrument measures what it intends to measure	Factorial structure (exploratory or confirmatory factor analysis, Rasch analysis)  A = confirmed, Rasch analysis is good  B = factorial analysis is good or Rasch has some problems  C = inadequate statistical analysis
	Types include: factorial structure (assess dimensionality); convergent correlations (comparisons with other measures); discriminant (differentiate based on known groups); hypothesis testing (outcomes support author’s hypothesis)	Convergent validity  A = >0.60  B = >0.30, <0.60  C = <0.30
		Discriminant validity  A = strong, in expected direction  B = moderate or conflicting evidence  C = weak
		Hypothesis testing A = clear hypothesis, evidence supportive B = clear hypothesis, evidence contradictory or unclear hypothesis with good supportive evidence of study purpose C = evidence does not support hypothesis or purpose
Item/Instrument bias	Assess in practical terms if individual questions or summary scores are biased for individuals with SCI	A = persons with SCI reviewed the instrument and acceptability is published B = there is adequate face-validity to support low bias C = bias is evident or tested
Measurement model	Examines if there are problems with floor effects (lowest level of ability) or ceiling effects (highest level of ability)	The instrument has scales or measures where 20% of persons with SCI are grouped at scoring extremes. Also can consider the score distribution:  A = no problems  B = few or marginal problems  C = substantial skewing of scales/measures

In addition to the SCIRE and Andresen’s criteria and definitions, we have included hypothesis testing to support instruments validity.⁽²⁶⁾ We investigated factorial structure in more detail. When domains were not expected to cover similar constructs, we reversed the Andresen criteria, considering poor correlation scores (r ≤0.30) excellent, moderate correlation scores (0.29–0.59) moderately discriminant, and high correlation scores (r ≥0.60) poor discriminant evidence. In known groups validity tests, little is known of these relationships in QOL, so known group tests could not be assigned A, B or C based on Andresen’s criteria. Groups are defined differently and different statistical methods are employed by each study’s author. We simply report groups demonstrating statistical differences in mean or total QOL scores.

When more than one paper provided validity or reliability values, a range of scores was assigned. Where more than one measurement was provided for reliability or validity within one domain (eg multiple item scores), a range was provided, and scores were assigned conservatively based on the lowest measured item.

RESULTS

Fourteen Level one studies reporting on 13 QOL instruments have been investigated with SCI populations: eight objective instruments, including the Patient Reported Impact of Spasticity Measure (PRISM),⁽²²⁾ the Quality of Well-Being scale (QWB),⁽⁶⁾ The Qualiveen,⁽²³⁾ the Sickness Impact Profile (SIP68),⁽²⁸⁾ the Short Form -36,⁽²⁹⁾ -36V,⁽¹⁹⁾ -12,⁽³⁰⁾ -6D,⁽³¹⁾ and five subjective instruments, including the Quality of Life Index (QLI),^(2,21) the Quality of Life Profile for adults with Physical Disabilities (QOLP-PD),⁽⁷⁾ the Satisfaction With Life Scale (SWLS),^(6,32) the Sense of Well-Being Index (SWBI), ^(9,33) and the World Health Organization Quality of Life –BREF scale (WHOQOL-BREF).^(1,34)

Table 2 presents instrument information, and table 3 provides information on the studies included in this review. Reliability is presented in table 4. Validity data is presented in tables 5 & 6. Table 7 presents a summary of measurement property scores, including results of the factor analyses and hypotheses testing. [insert table 2] [insert table 3]

Table 2.

QOL Instruments

Name	Description	Items	Domains (# of questions)	Scoring & Response	Measurement Model	Time Taken (mins)	Alternate Languages	Item Bias	Interview(I) or Self-Admin (SA)
OBJECTIVE TOOLS
Patient Reported Impact of Spasticity Measure (PRISM)	Addresses negative and positive impact of spasticity on QOL in SCI population	41	Societal avoidance/anxiety (11); Psychological agitation (5); Daily activities (6); Need for assistance/positioning (5); Impact on activities:+/− (4); Need for intervention (5); Social embarrassment (5)	5-point Likert scale: 0-never true for me; 1-rarely true for me 2-sometimes true for me 3-often true for me 4-very often true for me Subscale scores are obtained by averaging item scores and dividing by number of items Higher is unhealthier (more impact)	“Scores were somewhat skewed toward higher scores; that is, relative to the range of the scale, more persons scored in lower ranges (indicating less impact).”	not available	None	Developed in SCI population	SA
Quality of Well-Being Questionnaire-SA (QWB-SA)	Point-in-time preference measure designed to measure HRQOL	71	Symptoms & Problems (58); Mobility, Physical Activity, Social Activity (13)	0.0-death to 1.0-optimum health. Subtracts from 1.0. Higher is healthier	no floor & ceiling effects	<20	Various	Face validity supports low bias	SA
Qualiveen	Disease-specific perspective on QoL in SCI for urinary disorders	30	Limitations (9); Constraints (8); Fears (8); Feelings (5)	5-point Likert scales (0–4); total range 0–100 Tabulate total Higher is unhealthier	minimal	not available	Various	Developed in SCI population	I or SA
Sickness Impact Profile (SIP68)	Generic health status measure, measures health-related changes in behavior associated with the carrying out of daily activities	68	Somatic Autonomy (17); Mobility Control (12); Mobility Range (10); Social Behavior (12); Emotional Stability (6); Psychological Autonomy and Communication (11)	no=0, yes=1; total range 0–68 Yes responses are tabulated; can divide into SIPSOM, SIPPSY, SIPSOC subscales Higher is unhealthier	Ceiling effects MR (31.3%), ES (54%) & PAC (53.8%) domains	~15–20	English, Dutch	Scoring on one question adjusted for SCI	I or SA
Short Form 36 (SF-36)	Addresses basic human values relevant to QOL and well-being through individual domains and two global components	36	Physical Functioning (10); Role Limitations due to Physical Health Problems (4); Bodily Pain (2); General Health (5); Vitality (4); Social Functioning (2); Role Limitations due to Emotional Problems (3); Mental Health (5)	total range 0–100 Norm-based: general population mean score is 50, with each standard deviation 10. Can be divided into 2 summary scores: physical and mental, calculated by a system of + and − weights on domain scores Higher is healthier	Floor & Ceiling effect PF (12.2–24.2%; free-29.7%), RLP (28.1–36.3%; 22.5–54.4%); Ceiling effect SF (free-33.5%), RLE (63.8–75.3%)	<15	available in most major languages	Face validity supports low bias	I or SA
Short Form 36 Veterans/SCI (SF-36V)	Version of SF-36 designed for use in the disabled population. Physical Functioning section has been modified to accommodate SCI population	36	Physical Functioning (8)	each domain converted to range of 0–100 Divided into 2 summary scores: physical and mental component, are norm-based; general population score 50 and standard deviation of 10 Higher is healthier	“descriptive responses to the items showed a floor effect on many of the items”	not available	None	PF domain altered in SCI population	I or SA
Short Form 12 (SF-12)	A shortened version of the SF-36, used in population studies	12	Physical Functioning (2); Role limitations due to Physical Health problems (2); Bodily Pain (1); General Health (1); Vitality (1); Social Functioning (1); Role Limitations due to Emotional Problems (2); General Mental Health (2)	total range 0–100 Divided into 2 summary scores: physical and mental component, are norm-based; general population score 50 and standard deviation of 10 Higher is healthier	Summary scores free of floor & ceiling effects	~2–4	available in most major languages	Face validity supports low bias	I or SA
Short Form 6-Disability (SF-6D)	A 6-dimensional health state classification based on the SF-36	11	Physical Functioning (3); Role Limitation Physical (1); Role Limitations Emotional (1); Social Functioning (1); Pain (2); Mental Health (2); Vitality (1)	0.29 (the worst health state) - 1.00 (perfect or full health) Preference-based weights were assigned to each response; negative responses detract from perfect health score Higher is healthier	Floor effect PF(37%); Ceiling effect RLP&E(55%), SF(50%), P(36%), MH(35%)	not available	available in most major languages	Face validity supports low bias	I or SA
SUBJECTIVE TOOLS
Quality of Life Index (QLI)	Measures subjective QoL in terms of satisfaction	32–37	Health and Functioning (8); Social and Economic (8); Psychological and Spiritual (8); Family (8)	6-point Likert scales for importance and for satisfaction 1-very dissatisfied to 6-very satisfied and 1-very unimportant to 1-very important; total range 0–32 Weigh Satisfaction (S) scores with corresponding Importance (I) scores; 3.5 subtracted from S scores, raw I score used. Total and subscale scores tabulated Higher is healthier	None	~10	None for SCI version	SCI version evaluated by SCI patients	I or SA
Quality of Life Profile for Adults with Physical Disabilities (QOLP-PD)	A holistic approach to QoL that empowers individuals where elements of QOL are the same for people with and without disabilities, but each may address issues differently; questions address aspects of daily life	102	Being (32): Physical, Psychological, Spiritual; Belonging (37): Physical, Social, Community; Becoming (33): Practical, Leisure, Growth	5-point Likert item scales 1-not at all satisfied to 5-extremely satisfied and 1-not important to 5-very important; Weigh Satisfaction and Importance scores for each item; 3 points are subtracted from S scores, raw I scores used Higher is healthier	none reported	not available	None	Developed in disabled and SCI population	I or SA
Satisfaction With Life Survey (SWLS)	Addresses life satisfaction as a whole, reflecting a global perspective of individual’s values	5	In most ways my life is close to ideal; The conditions of my life are excellent; I am satisfied with my life; So far I am getting the important things I want in life; If I could live my life over, I would change almost nothing	7-point Likert scale: 1-strongly disagree to 7-strongly agree; total range 5–35 Global score is computed Higher is healthier	Floor effects seen on some items	<5	multiple	Face validity supports low bias; some questions may be inappropriate for SCI	I or SA
Sense of Well-Being Index (SWBI)	Measures subjective QOL for people with disabilities in work rehabilitation, addresses successful rehabilitation beyond objective employment outcome	26	Physical well-being and associated feelings about self (6); Psychological well-being (7); Family and social well-being (6); Financial well-being (8)	4-point Likert scale 1-strongly disagree to 4-strongly agree Tabulate total and domain scores Higher is healthier	none reported	“brief”	No	Altered for and evaluated in SCI population	I or SA
World Health Organization Quality of Life (WHOQOL-BREF)	Instrument that conceptually fits with the WHO definition of QOL	26	Physical Health/Capacity (7); Psychological Health/Well-Being (6); Social Relationships (3); Environment (8); Overall QoL (1); General Health (1)	5-point Likert scales (1–5), total scale of 0–100 Domain scores calculated by multiplying mean of facet scores by 4 (4–20), and transformed onto a scale of 0–100 Higher is healthier	None; floor effect in 1 item: Mobility (29.7%)	not available	available in most major languages	Face validity supports low bias	SA

SIPSOM = Physical dimension of functional status; SIPPSY = psychologic dimension of functional status; SIPSOC = social dimension of functional status

Table 3.

Summary of included papers

Author	Measures	n	Sample characteristics (mean+-sd)	Purpose	Procedure
Cook et al. (2007)(22)	PRISM	32 (development) 180 (validity and reliability study)	15+/−11 yrs of injury; 5 2+/−12 yrs of age; USA veterans	To develop and validate the PRISM.	Factor analyses and content validity was done to develop the PRISM. One week test-retest and internal consistency were calculated for reliability and discriminative ability among known groups was done to validate the scale.
Andresen et al. (1999)(4)	QWB-SA, SF- 36, SF-12	183	17.9+/−11.36 yrs of injury; 50.52+/−12.73 yrs of age; USA veterans	To evaluate the performance of health related quality of life instruments.	Cross-sectional study to assess the instruments’ respondent burden and acceptability, pattern of correlations, floor and ceiling effects, and discriminative ability among known groups.
Costa et al. (2001)(23)	Qualiveen	281	11 yrs of injury; 41 yrs of age; France	To develop and validate the Qualiveen for SCI patients with urinary difficulties.	Through patient interviews an item pool was generated. After item-reduction, the Qualiveen was psychometrically assessed via multi-trait and principal component analysis. Test-retest reliability was also evaluated.
Post et al. (1996)(28)	SIP68	315	3.6+/−1.9 yrs of injury; 39.4+/−12.5 yrs of age; Netherlands	To validate the SIP68.	Cattell’s similarity index was used to assess the expected theoretical factor structure. Criterion validity was assessed with comparisons to the Barthel Index, Life Satisfaction Questionnaire, and social functioning. Chronbach’s alpha was calculated to evaluated internal consistency.
Forchheimer et al. (2004)(16)	SF-36	215	1–13 yrs of injury; 34.5 yrs of age; USA	To evaluate the applicability of the SF-36 for assessing health-related quality of life.	To test the hypotheses that: 1) the SF-36’s physical and mental component scores are two distinct constructs; and 2) that the relationship between the component scores and neurologic impairment would support both convergent and divergent validity. Internal consistency was also calculated.
Lin et al. (2007)(38)	WHOQOL- BREF, SF-36	187	7.4 yrs of injury; 42.9 yrs of age; Taiwan	To compare the psychometric performance of the WHOQOL-BREF and the SF-36.	Internal consistency, intrainterviewer and interinterviewer test-retest reliabilities, convergent and known-groups validities, and the responsiveness between the WHOQOL-BREF and the SF-36 were compared.
Luther et al. (2006)(19)	SF-36V	359	Post-discharge; all ages; USA veterans	To develop a SCI specific physical functioning scale on the SF-36V.	A pool of items was developed from focus groups. Exploratory factor analysis was conducted to identify items loading on how many factors. IRT analyses were further conducted on each item. Internal consistency, convergent, divergent validity were also assessed.
Lee et al. (2008)(18)	SF-6D	305	1 month-61 yrs of injury; 43.5+/−13.5 yrs of age; Australia	To evaluate the SF-6D’s discriminative ability and determine its responsiveness to clinically important change. The external criterion used to define clinically important change is the occurrence of a urinary tract infection.	Discriminative ability was assessed via known groups. Responsiveness was determined by minimal important differences (MID), or the smallest difference in score that the patient perceives as beneficial.
Jang et al. (2004)(1)	WHOQOL- BREF	280 (including 111 SCI respondents)	6+/−6 yrs injury; 40+/−13 yrs of age; Taiwan	To validate the WHOQOL-BREF.	Multitrait analysis was used to confirm the domain structure of the WHOQOL-BREF. The measure’s discriminative ability was evaluated in its ability to distinguish between known groups. Internal consistency (Chronbach’s alpha) was also calculated.
Chapin et al. (2004)(9)	SWBI	132	15.21+/− 11.63 months of injury; 45.82+/−15.67 yrs of age; Canada	To assess the validity of the SWBI.	Factor analyses was done to validate the original SWBI factors among SCI. Concurrent validity was completed via correlation with the WHOQOL- BREF
Dijkers (1999)(6)	SWLS	2,183	Various points post-injury; all ages; USA	To validate the SWLS.	Follow-up of subjects studied prospectively since onset of injury (1–20 years). Predictors of subjective well-being were correlated with the SWLS.
May & Warren (2001)(21)	QLI	11	10.5 yrs of injury; 33.1 yrs of age; Canada	To modify and validate the QLI.	A qualitative study. The meaningfulness of the QLI items was evaluated among the SCI sample through “think out loud” interviews. The structure of the QLI was assessed by a “free sort” exercise.
May & Warren (2002)(2)	QLI	98	15.5 yrs of injury; 45.3 yrs of age; Canada	To validate the QLI.	To test the hypotheses that there would be no significant relationship between QOL and 1) motor function, 2) functional independence; that significant relationships exist between QOL and 3) community integration, 4) self-esteem and 5) locus of control; and that the factor structure would be similar to the original four factor structure.
Renwick et al. (2003)(6)	QOLP-PD	40	2–30 yrs of injury; 35.85+/19.29 yrs of age; Canada	To validate the QOLP-PD.	Internal consistency and correlations between sub- scale scores and the total score are only available for the SCI group.

Table 4.

Reliability

	Alpha	ICC or Kappa
Instrument	Internal Consistency	Test-retest	Intra-interviewer	Inter-interviewer
Objective tools
PRISM	0.74–0.96(22)	0.82–0.91(22)
Qualiveen	0.8–0.85(23)	0.85–0.92(23)
SIP-68	0.92(28) 0.68–0.91(28)
SF-36	0.76–0.9(16)
	0.72–0.98(38)		0.71–0.99(38)	0.41–0.98(38)
SF-36V	0.9(19)
Subjective tools
QOLP-PD	0.84–0.98(7)
SWLS		0.39–0.65(6)
SWBI	0.79–0.88(9)
WHOQOL-BREF	0.75–0.87(38)		0.84–0.98(38)	0.56–0.95(38)
	0.54–0.78(1)

Table 5.

Factor Analyses – interitem or subscale correlations

Instrument			Correlations
Objective tools
PRISM	Subscale correlations	Social avoidance/anxiety	0.07–0.73(22)
		Psychological agitation	0.12–0.73(22)
		Daily activities	0.29–0.63(22)
		Need for assistance/positioning	0.27–0.63(22)
		Need for intervention	0.48–0.65(22)
		Social embarrassment	0.26–0.72(22)
Qualiveen	Subscale correlations		0.12–0.77(23)
SIP-68	Subscale correlations		0.44–0.80(28)
	Total	Subscale	0.08–0.67(28)
SF-36	Physical Component Score	Mental Component Score	-0.075(16)
SF-36V	Physical functioning	Role-physical; bodily pain; general health domains	0.29–0.55(19)
		Physical Component Score	0.64(19)
		Vitality; social functioning; mental health domains	0.18–0.32(19)
		Mental component score	0.16(19)
Subjective tools
QLI	Total	Satisfaction score	0.98(21)
		Importance score	0.47*(21)
QOLP-PD	Adjusted Total Score	All domains and sub-domains	0.63–0.88(7)
SWBI	Subscale correlations		0.37–0.58(9)
WHOQOL-BREF	Overall QOL & General Health	All domains	0.41–0.59(1)
	Physical Health items	Physical domain	0.55–0.76(1)
		All other domains	0.14–0.61(1)
	Psychologic Health items	Psychologic domain	0.59–0.73(1)
		All other domains	0.33–0.59(1)
	Social Relationship items	Social domain	0.65–0.77(1)
		All other domains	0.28–0.61(1)
	Environment items	Environment	0.52–0.75(1)
		All other domains	0.16–0.56(1)

^*After exclusion of an outlying point

Table 6.

Validity: Multitrait Multimethod

Instrument		Validity		Discriminant Validity
		Excellent or Moderate correlation	Poor or No correlation
Objective tools
QWB	Total score	IADL (r = −0.454)(5) SF-36 physical summary (r = 0.417)(5) SF-12 physical summary (r = 0.34)(5)	SF-36 domains (r = 0.044–0.29)(5) SF-12 Mental summary (r = 0.164)(5) BRFSS items (r = −0.25 – 0.182)(5)	Total	para/quad, upper body difficulty(5)
Qualiveen				Domains	SQLP how well patients urinate, patient satisfaction with urination, time taken to urinate(23)
SIP68	All domains, Overall	BI (r = −0.91–0.41)(28) LSQ (r = −0.53–0.32)(28)	LSQ vs SIP Mobility Control (r = −0.22)(28) BI vs SIP 68 Emotional stability(r = −0.11), Psychic autonomy & Communication (r = − 0.21)(28)	Domains	vocationally active, level of lesion(28)
SF-36	All domains	WHOQOL-BREF domains (rs = 0.33–0.78) (38) RS (rs = 0.32–0.72)(38) BRFSS items(r = −0.795 – 0.3083; 0.389 – 0.789) (5) SF-36 physical functioning, social functioning, mental health vs IADL (r = −0.454–0.308) (5)	QWB(r = 0.044–0.261)(5) IADL (r = −0.3–0.201) SF-36 Role limitations: emotional vs WHOQOL-BREF Overall QOL & General Health (0.3), Social Relationships(r = 0.24)(38)	Domains	age, ASIA impairment severity, employment status, level of injury, marital status, self-care ability(38), severe work disability, upper body difficulty(5)
			SF-36 physical functioning vs BRFSS items(r = −0.226–0.088) SF-36 role limitations: physical(r = −0.219), general health(−0.295), social functioning(r = −0.293), role limitations: emotional(r = −0.29) vs BRFSS days without enough sleep(5)
	Physical component score	SF-12 Physical Health Summary (r = 0.799) (5) QWB (r = 0.417)(5) IADL (r = −0.357)(5) BRFSS items good days (r = 0.443), days full of energy (r = 0.489), poor physical health days (r = −0.458)(5)	BRFSS other items (r = −0.354 – 0.217) (5)
	Mental component score	BRFSS items(r = −0.761 – 0.427)(5) SF-12 Mental Health summary score(r = 0.922)(5)	QWB(r = 0.116)(5) IADL(r = −0.262)(5)
SF-36V	Physical functioning	SCDRQ ADL(r = 0.63)(19) SCDRQ IADL(r = 0.7)(19)
SF-12	Physical Health Summary	SF-36 physical component score(r = 0.779)(5) QWB(r = 0.34)(5) BRFSS items good days (r = 0.306), days full of energy (r = 0.333), poor physical health days(r = − 0.324)(5)	IADL(r = −0.272)(5) BRFSS other items(r = −0.2 – .064)(5)	Physical Health Summary, Mental Health Summary	upper body difficulty, severe work disability(5)
	Mental Health Summary	BRFSS items(r = −0.799 – 0.37, 0.639 – 0.665)(5) SF-36 Mental Component Score(r = 0.922)(5) IADL(r = −0.37)(5)	QWB(r = 0.164)(5)
SF-6D				Total	employment status, tetra/para, time since injury(18)
Subjective tools
QLI	Total Score	Reintegration to Normal Living index(r = −0.654)(3) Rosenberg’s Self-Esteem Scale(r = 0.609)(2)	Rotter’s Internal-External scale of locus control(r = −0.024)(2)
SWLS				Total	CHART scores, employment status, FIM motor score, FIM sociocognitive score, level of education, level of injury, marital status, number of hospitalizations in the last year, number of pressure ulcers, race/ethnic group, sex, years since injury (6)
SWBI	Psychological well-being	WHOQOL-BREF Psychologic(r = 0.75)(9)		Domains	education, employment status, family income, marital status, perceived socio-economic status, years since disability onset (9)
	Financial well-being	WHOQOL-BREF environment(r = 0.59)(9)
	Family and social well- being	WHOQOL-BREF social relationship(r = 0.45)(9)
	Physical well-being	WHOQOL-BREF physical health(r = 0.63)(9)
WHOQOL-BREF	All domains	RS(rs = 0.54 – 0.73)(38) SF-36 domains(rs = 0.33 – 0.78)(38)	WHOQOL-BREF overall QOL & general health(rs = 0.3), social relationship domains(rs = 0.24) vs SF-36 Role Emotional(38)	Domains	age, employment status, level of injury, marital status, self-care ability,(38) SCI to non-SCI(1)

BI = Barthel Index; LSQ = Life Satisfaction Questionnaire; BRFSS = Centers for Disease Control and Prevention Behavioral Risk Factor Surveillance Survey; IADL= Instrumental Activities of Daily Living.

Table 7.

Summary^*

Instrument	Number of studies	Measurement model	Item bias	Reliability		Validity
						Hypothesis Testing	Factor Validity
				Internal Consistency	Test-Retest		Factor Analysis	Convergent	Discriminant
OBJECTIVE TOOLS
PRISM	1	B	A	B	A	B	A	B	A
QWB	1	A	B	-	-	C	-	-	-
Qualiveen	1	A	A	A	A	A	B	B	B
SIP68	1	B	A	A–C	-	A	A	B	A–C
SF-36	3	B (domains); A (sub-scores)	B	B	B	A–B	-	-	A
SF-12	1	A	B	-	-	C	-	-	-
SF-36V	1	C	A	A	-	B	A	A–C	A–B
SF-6D	1	C	B	-	-	A		-	-
SUBJECTIVE TOOLS
QLI	2	A	A	-	-	C	B	A–C	-
QOLP-PD	1	-	A	A	-	C	-	A	-
SWLS	1	B	B	-	C	C	A	-	-
SWBI	1	-	A	B		A	A	-	B
WHOQOL-BREF	2	A	B	B–C	B	A–C	-	B	B–C

^*Ranges are presented where information from more than one study was available

Objective QOL instruments

The PRISM measures QOL relative to spasticity,⁽²²⁾ with six domains addressing negative consequences of spasticity, and one, the positive impact (PI). Negative PRISM QOL scores worsened in a significant manner with increasing severity of negative spasticity symptoms, as expected by the authors, and persons reporting that benefits of spasticity outweigh problems, scored higher on the PI scale (p<0.001). However, greater negative interference did not correlate to higher negative impact scores. The PRISM domains correlated moderately to one another (r = 0.45–0.73), covering related topics such as need for assistance/positioning and social embarrassment, with the exception of the Positive Impact scale (r = 0.07–0.29). Factor analysis confirmed that the domains are addressing distinct facets of spasticity-related QOL. ⁽²²⁾

The QWB measures health status and well-being;⁽²⁷⁾ it provides quality adjusted life years for health economic analyses. In persons with SCI, this generic measure, did not correlate well with other QOL measures such as the SF-36, (r = 0.044–0.29)⁽⁵⁾ and reliability has not been established in an SCI population.

The Qualiveen measures the impact of urinary disorders on QOL as well as overall ratings of QOL in persons with SCI. ⁽²³⁾ Qualiveen QOL scores decreased as urinary problems increased. (p<0.0001–0.01) The Qualiveen was originally developed in French for the SCI community. The instrument demonstrated excellent reliability in the SCI population. (α = 0.80–0.85) ⁽²³⁾ (table 4)

The SIP68 is derived from the original 136-question version SIP136.^(20,35) The SIP68 showed high correlation with physical measurements such as the Barthel ADL Index, (r = −0.91–0.41).^(28,36) However, Post et al. (1996) argued that, because SIP68 correlates highly with a measure of life satisfaction, it must be measuring a broader concept than health state and self-care ability.⁽²⁸⁾ Total and subscore reliabilities were high for the SIP68 (α = 0.8–0.92), but the emotional stability domain demonstrated consistently low reliability in the SCI population (α = 0.68).⁽²⁸⁾

The SF-36 is a widely used HRQOL instrument. It has been translated and widely promoted by the International Quality Of Life Assessment project;⁽³⁷⁾ translations have been developed for more than 60 countries. The SF-36 has been validated in multiple SCI studies.^(5,16,38,39) Data strongly supports authors’ hypotheses that the mental and physical components would correlate to similar domains on other QOL instruments,^(5,38) but not to one another.⁽¹⁶⁾ Factor analysis has been conducted extensively in other populations; see www.sf-36.org. Reliability was moderate to high for the SF-36 (α = 0.72–0.98)^(16,38) except the general health item (interinterviewer ICC = 0.41). The SF-36 was shortened to contain just 12 questions (SF-12) and only provide mental and physical subscores. The SF-12 has not been widely used and validated in the SCI population, but has shown expectedly high correlation with the SF-36 (r = 0.78–0.99).^{(5) (38)} Reliability was not examined in the SF-12.

The Veterans Health Administration version of SF-36 (SF-36V) modified the Physical Functioning (PF) domain for SCI populations. The modifications generally involved substituting activities more appropriate to SCI clients, such as “climbing… wheel chair ramps” rather than stairs, or “getting up and down from a curb.”⁽¹⁹⁾ The SF-36V supported the authors’ hypothesis that it more accurately reflects SCI QOL, demonstrating internal validity with the physical but not the mental component score. It was necessary to alter the wording of the questions based on SCI consumer input more than anticipated, and mobility was rated as if respondents were using their assistive devices. Internal consistency was high (α = 0.90). ⁽¹⁹⁾

A preference-based health measure, the SF-6D, has also been derived from the SF-36 and SF-12.⁽⁴⁰⁾ Its usefulness was evaluated by assessing its responsiveness to urinary tract infection. It could discriminate between SCI and non-SCI respondents; however, floor effects were seen in the physical domain (37%), and reliability was not examined.⁽¹⁸⁾

Subjective QOL instruments

The Ferrans and Powers QLI addresses overall satisfaction with life, and attempts to cover all facets of QOL.^(41,42) While the language of the SCI version of the instrument was well received by SCI clients,⁽²¹⁾ and the satisfaction scores agreed with the overall score,(r = 0.98)⁽²⁾ the domain structure did not fit with subject interpretations⁽²¹⁾ or factorial analysis.⁽²⁾ Further, the correlation of the importance scores was very low (r 0.47).⁽²⁾ As expected, QLI scores correlated to both community integration (participation) (r = −0.65) and self esteem (r = 0.61) but not to body functions and structure or the level of activity. The instrument was unexpectedly not correlated to locus of control, (r = −0.02) and reliability was not examined.⁽²⁾

The QOLP-PD takes an extremely subjective approach to QOL assessment. It holds that QOL elements are common to most human beings, with and without disabilities, but that adults with physical disabilities may address life issues somewhat differently. Reliability (α = 0.84–0.98) and construct validity(r = 0.63–0.88) are both excellent. ⁽⁷⁾

The SWLS contains five statements about life satisfaction: three set in the present, one in the past, and one in future. It is “one of the few existing instruments that measure life satisfaction as a global entity, rather than requiring subjects to rate their satisfaction with each of a number of domains of life.” ⁽⁵⁾ In accordance with the authors’ hypotheses, impairment (level of injury), number of hospitalizations, and the number of pressure ulcers related to life satisfaction (p<0.05), but completeness of injury did not. Two week test-retest was moderate to low (ICC = 0.39–0.65).⁽⁵⁾ The SWLS reflects general life satisfaction, but is not detailed as to specific aspects of QOL.

The SWBI was developed to assess QOL in disabled populations in vocational rehabilitation programs. The authors argue that, to achieve maximum potential in the rehabilitated worker, rehabilitation programs must assess overall QOL, both subjective and objective, as “research indicates that there is a dynamic interaction between quality of work life and quality of life in general.” ⁽⁹⁾ The authors correctly hypothesized that the revised SWBI for SCI would have similar measurement properties to the original, would correlate well with the WHOQOL-BREF,(r = 0.45–0.75) and would show similar patterns of known group validity to other QOL instrument in the literature.⁽⁹⁾

The WHOQOL assessment was developed as an international effort to create a cross-cultural, cross-population QOL measure based on a generic theoretical model of QOL. ^(34,43) The short version, the WHOQOL-BREF, has been assessed by multiple authors. ^(1,9,38,44) Population-specific versions exist, such as the Taiwan/Hong Kong version with two additional questions of local cultural importance.⁽³⁸⁾ Although sometimes considered a HRQOL instrument, many questions rate individual subjective satisfaction, thus covering both objective and subjective components of QOL. The WHOQOL-BREF generally supported authors’ hypotheses that it would demonstrate item-domain validity,(r = 0.41–0.77)⁽¹⁾ correlate in appropriate domains with other QOL measures such as SF-36,(r_s = 0.33–0.78)^(38,45) and differentiate between sub-groups such as employment, self-care ability, age, marital status, and level of injury.⁽³⁸⁾ Reliability was moderate to high, (α = 0.74–0.87) with the exception of the social relationships domain, which was consistently lower than the other domains (0.54).^(1,38)

Discussion

Definition of QOL

It is evident that there are currently as many definitions of QOL as there are instruments measuring it. We have examined existing literature on 13 QOL instruments that have been investigated in SCI populations. By assembling these instruments for this population, conclusions can be drawn on the broad themes found in QOL investigation, such as subjective versus objective measurement, approaches to QOL definition, and lack of data on cause and effect in SCI QOL.

Measurement Properties of Instruments

Generally, sufficient investigation has been done to validate the use of only a few of the QOL instruments with SCI populations. The WHOQOL-BREF and SF-36 have been extensively used and validated. In the SF-36, concern has been expressed in the SCI community regarding the appropriateness of the use of the term “walking” in the mobility-related physical questions of the SF-36.^(5,19) This concern has been addressed in the SF-36V, which requires further investigation prior to wide-spread use with SCI populations. The SF-12 and SF-6D also exhibit certain SCI bias and floor effects^(5,18) that could easily be removed if they were derived from the SF-36V, as opposed to the original SF-36.

The Qualiveen and PRISM have performed well in all measurement properties,^(22,23) likely due to the clarity of results obtained from objective QOL measures, which can be strongly and concretely correlated to health state. Both could use further investigation in SCI populations.

For objective QOL, the SIP68, and for subjective, the QOLP-PD and the SWBI all have very positive supportive evidence and face validity, appropriate for their continued use.^(7,9,20) Again, all three require much more investigation, especially those measuring subjective QOL, which are more difficult to validate, given the theoretical nature of the underlying construct.

Disappointing results were obtained for the QLI, the QWB and the SWLS. ^(2,5,6) The QLI likely requires alteration to the structure of the importance scale scoring, and potentially domain rearrangement before widespread use in SCI populations. The QWB preference-weighted scoring approach, weighing certain symptoms more heavily than others, is founded on data from the general population. It measures HRQOL from a “decision theory approach”, where differently-weighted symptoms contribute to one final score, which can be applied to any population.⁽⁴⁶⁾ This is distinct from the approaches of other QOL instruments, where a profile is generated composed of measurements in several domains; the QWB correlated only moderately to the physical domain of the psychometric SF-36 instrument.⁽⁵⁾ The QWB tells health-care providers very little about the HRQOL of their individual SCI client, as it is intended to offer inter-population comparison, with less sensitivity to clinical change.⁽⁴⁶⁾ With respect to the SWLS, it is possible that the brevity and generality of its approach, as well as the wording of several of the questions (eg “If I could live my life over, I would change almost nothing”) weakens its applicability with SCI population.

Subjective QOL issues

In the field of SCI QOL research, there is controversy over the appropriateness of objective QOL measurements. This is due to the assumptions these measurements impose on individuals with different life circumstances and ability levels, namely, that all individuals prioritize common life domains and goals, especially those related to measureable outcomes such as financial gain or physical strength, and that success and achievement in these domains and goals is directly proportional to happiness and life satisfaction. Not only this, but it had been found that injury-specific variables such as level or severity of injury do not always affect objective QOL.^(5,18) As an alternative, subjective QOL purports to measure outcomes through the point of view of the individual, that can not necessarily be broadly generalized. This issue with the subjective instruments is addressed in various ways. In the QOLP-PD development, Renwick et al. (2003) suggested that all individuals value similar elements of life, but may address or achieve these differently.⁽⁷⁾ In this and several other subjective QOL instruments, satisfaction with items scores are weighted by scoring the importance of these items to the individual. ^(2,7) Alternatively, instruments such as the SWLS address QOL without splitting it into domains or questioning specific aspects of life, resulting in a measurement of overall satisfaction with life only.

While most objective QOL measures have existed for much longer, and thus have much more published data and utilization, many authors now suggest the use of subjective QOL measures as more appropriate in individuals with SCI. ^(6,7,9) Scores in objective QOL domains are found to be lower in SCI than in the general population,^(1,18) while some domains of subjective QOL are equal to the general population, and some are higher.⁽⁴⁷⁾ Item bias scores for SCI were higher in the subjective instruments, while measurement model scores were higher in the objective instruments. These trends would seem to reflect the differences in QOL models, where subjective instruments are more highly attuned to the individual’s situation, and subjective QOL can vary greatly between individuals. While objective QOL is more easily measured, such instruments have the potential to miss many aspects of the individual’s life.

Clearly, objective and subjective QOL instruments are measuring different constructs, and thus have different conceptualizations of QOL. It may be that, like the mental and physical component scores of the SF-36, both contribute equally, rather than solely, to the overall QOL score. Or, it could be that, similar to satisfaction and importance scores in many of the instruments, one should be weighted against the other. A mixture of subjective and objective approaches could resolve the existing debate on which is the more appropriate approach to QOL research, or, as Fuhrer stated, “measures of subjective well-being should be viewed as being complementary with objective indices of people’ s functioning and life status.”⁽¹⁰⁾

Conclusions

Overall, there is a wealth of data on SCI QOL. There are numerous promising instruments to measure QOL. Unfortunately, because of a lack of consistent results and definitions, our knowledge pertaining to the QOL among individuals with SCI is still limited. It is important to keep in mind that we are attempting to perform a comparison of different measurement instruments of QOL that are based on different definitions of QOL. A more concrete, universal definition of QOL is required, as is further investigation on the causative and related effects of different aspects of the SCI client’s life on QOL. Known group associations that are examined in a systematic and consistent manner between studies and populations would provide valuable information. With a clear definition of QOL, this type of investigation could be undertaken without the excessive contradictions that exist in the literature at present. In terms of the instruments included in this review, the disease state-specific HRQOL Qualiveen, PRISM, and SIP68 performed very well. The longer, more varied HRQOL SF-36 and subjective WHOQOL-BREF performed moderately well in all areas, with the added bonus of their wide-spread use and the wealth of evidence supporting their outcomes. Several newer subjective QOL instruments also performed very well, but will need further investigation, including the SWBI, and the QOLP-PD. The remaining instruments lacked either SCI-appropriate structure, language, or investigation.

Pending further investigation of some of the very promising but recently developed instruments, we would recommend the use of the WHOQOL-BREF, as it addresses both objective and subjective QOL, is based upon an international effort to clearly define QOL, and has been well studied in SCI populations with acceptable results. The SF-36V or SIP68 as measures of HRQOL, or the QOLP-PD or the SWBI as measures of subjective QOL, also show promise but require further investigation prior to using with confidence. In the context of clinical practice or research, investigators must choose tools based on practice/purpose, and explicitly state their concept of the definition of QOL.