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. Author manuscript; available in PMC: 2019 Jul 30.
Published in final edited form as: Schizophr Res. 2018 Feb 19;197:150–155. doi: 10.1016/j.schres.2018.02.009

Associations of Independent Living and Labor Force Participation with Impairment Indicators in Schizophrenia and Bipolar Disorder at 20-Year Follow-Up

M Strassnig 1,*, R Kotov 2, L Fochtmann 2, M Kalin 3, EJ Bromet 2, PD Harvey 4,5
PMCID: PMC6098976  NIHMSID: NIHMS947905  PMID: 29472164

Abstract

Background

Since the Iowa 500 study, residential and occupational status have been frequently used as indicators of everyday achievements in research on schizophrenia and bipolar disorder. The relationships of residential and occupational status with impairment in multiple domains including physical health indicators across these two diagnoses, however, have rarely been studied. We examined these relationships at the 20-year follow-up assessment of a first-admission sample.

Methods

We included 146 participants with schizophrenia and 87 with bipolar disorder with psychosis who participated in the 20-year follow-up of the Suffolk County Mental Health Project. In addition to interviewer-based ratings of employment and residential independence, we examined self-reported impairment derived from the WHODAS, standard measures of current psychopathology, indicators of obesity, as well as performance-based measures of physical and cognitive functioning.

Results

Participants with bipolar disorder were more likely to live independently and be gainfully employed; they also performed significantly better on each indicator of impairment apart from balance ability. In both groups, unemployment, but not residential independence, was associated with greater self-reported disability on the WHODAS. Residential independence, gainful employment, and subjective disability were also associated with better physical functioning. Across the two groups, psychiatric symptoms and physical functioning were the major determinants of subjective disability.

Discussion

People with psychotic bipolar disorder were more likely to be gainfully employed and living independently than participants with schizophrenia but as a group, much less frequently than population standards. Interventions aimed at physical fitness may have the potential to improve both objective functioning and perceived disability.

Keywords: Schizophrenia, Disability, Obesity, Symptoms, Cognition, Physical Functioning

Background

Severe and persistent mental illnesses, including schizophrenia and bipolar disorder, are among the leading causes of disability (Murray & Lopez, 1997; Gonzalez-Medina et al., 2012). Despite the striking nature of psychotic and manic symptoms, the most significant impairments that arise after the acute phase include limitations in critical areas of everyday functioning, such as the ability to live and work independently (Morrison et al., 1972; Bowie et al., 2006; Tabares-Seisdedos et al., 2008; Harvey & Strassnig, 2012). Global impairments in functioning are thought to be less severe in bipolar disorder when compared to schizophrenia but significant enough to have important adverse long-term implications (Bowie et al., 2010; Mausbach et al., 2010). Specifically, 70-90% of individuals with schizophrenia and 40-60% of those with bipolar disorder have been reported to have challenges with independence in residence and gainful employment (Huxley & Baldessarini, 2007; Leung et al., 2008; Marwaha et al., 2013; Twamley et al., 2002; Lee et al., 2015) despite generally successful treatment of psychosis and mood dysregulation during the earliest phases of illness (Tohen et al., 2003; Robinson et al., 2004).

The known components of impairment in schizophrenia and bipolar disorders include psychiatric symptoms, cognition, and functional skills (Bowie et al., 2010). Impairments in everyday functioning, specifically the ability to maintain a residence and gainful employment are predicated by different skill sets and may be further differentiated by the influence of a diagnosis of schizophrenia or bipolar disorder (Bowie et al., 2010; Harvey et al., 2012; Strassnig et al., 2015). Moreover, even with psychiatric symptoms, cognition and functional skills accounted for, large proportions of the predictive variances for reaching independence in residence and employment are unknown (Harvey & Strassnig, 2012), including potential similarities and differences between schizophrenia and bipolar disorder. To that end, we recently introduced physical health limitations, prevalent in schizophrenia and bipolar disorder 18, as novel impairment indicators: we showed that health limitations, particularly increased waist circumference and simple measure of physical functioning are associated with physical limitations that can impinge on the ability to carry out everyday activities (Strassnig et al., 2017). Whether physical limitations, such as obesity and reduced physical capacity and skills, are associated with other aspects of disability including self-reported impairment as measured by the WHODAS 2.0 and whether there are any differences between the schizophrenia and bipolar disorder groups in self-reported outcome when accounting for the range of possible impairment indicators is currently unknown.

The purpose of this report is to understand the relationships of 1) residential and employment status with multiple aspects of disability including physical limitations and secondarily 2) the associations among the various indicators of impairment with these outcomes across assessment strategies. Also, the availability of self-reported disability data allowed us to examine the association between objective functional outcomes and subjective evaluations of disability. The objective impairment indicators were also examined for their correlations with subjective disability. The data were derived from a well-characterized sample of individuals with bipolar and schizophrenia spectrum disorders assessed 20 years after their first hospitalization for psychosis. Most available cohort studies, especially those with durations over 10 years, have focused on aspects of everyday functioning in schizophrenia only (Hegarty et al., 1984; Harrison et al., 2001; Hill et al.,. 2012; Jaaskelainen et al., 2008). Only a small number have examined other psychotic disorders, such as bipolar disorder (Hegelstad et al, 2012; Morgan et al,. 2014; Harrow et al., 2005) and generally not with a comparative focus on schizophrenia.

Methods

The sample is part of the Suffolk County Mental Health Project, a county-wide treatment sample recruited during their first admission for a psychotic disorder between 1989 and 1995 (for details, see Bromet et al., 1992; Bromet et al., 2005; Kotov et al., 2017). Baseline inclusion criteria were age 15-60 years, residence in Suffolk County NY, and psychosis not due to a medical condition or substance abuse; exclusion criteria were a psychiatric hospitalization more than 6 months before the index admission, low intellectual ability (IQ < 70), incapacity to provide informed consent, and being a non-English speaker. The data for the current analyses were obtained at a followup assessment 20 years after the index admission. The Institutional Review Board of Stony Brook University approved the study annually. Written informed consent was obtained at follow-up assessment. On the basis of the SCID interviews, medical records information, and interviews with the subjects’ relatives, DSM-IV consensus diagnoses were reached for each participant. For the current analysis, we used the 10-year follow up diagnosis (the most recent diagnosis on file) and we selected participants with schizophrenia/schizoaffective disorder (SCZ) (n=146) and bipolar disorder (BP) (n=87). We excluded patients with psychosis related to depression, substance use, and ‘other’ psychoses. A flowchart of participation in the larger study is available; attrition was random, that is, the number of assessments was not associated with age, sex, negative symptoms, positive symptoms, employment, independence in living, homelessness, or baseline diagnosis. Nonresponse was primarily accounted for by refusal to participate and loss to follow up. (Velthorst et al, 2017).

Measures

Diagnosis

The Structured Clinical Interview for DSM-III-R (Spitzer et al., 1990) was administered at the baseline, 6 month, and 2-year follow-ups, and the SCID for DSM-IV was administered at year 10 (Bromet et al., 2011). Based on the SCIDs, medical record information, and interviews with significant others, longitudinal DSM-IV consensus diagnoses were reached by study psychiatrists for each participant. For the current analysis, we used the 10-year diagnosis.

Everyday Functioning

Background information about residential and occupational status was obtained during the SCID Overview and in a separate assessment of quality of life. Interviewers then coded two measures: independence in residence (defined here as living fully independently without external support vs. living in households of relatives, group homes, or supported settings) and gainful employment (defined as competitively obtained part- or full-time employment vs. not employed in a steady job or participating in supported employment). Spouses of employed individuals were coded as living independently. Individuals living with their parents were coded as not living independently as the average age of the participants was in their 40’s.

Self reported Disability

The self-report WHODAS-12 (World Health Organization Disability Assessment Schedule 2.0) (Ustun et al., 2010) assesses six areas: understanding and communication, self-care, mobility, interpersonal relationships, work and household roles, and community participation. The WHODAS 2.0 has good internal consistency, test-retest reliability, and concurrent validity (Andrews et al., 2009). A WHODAS total score was derived by adding the 12 individual item scores.

Symptoms, Cognitive Performance, and Physical Functioning

Mental health symptom measures included: the Scale for Assessment of Negative Symptoms and Scale for Assessment of Positive Symptoms (Andreasen, 1984a, 1984b); the Brief Psychiatric Rating Scale (Worener et al., 1988), the Hamilton Depression Rating Scale (Hamilton, 1960), a composite cognitive measure (see below); waist circumference, an indicator of obesity/metabolic syndrome; and two physical functioning measures, chair rises and balance. The latter tasks are part of the Short Physical Performance Battery (Guralnik et al., 1994; Guralnik et al, 1996) a widely used test in aging research (Rikli & Jones, 1999). The tests were modified to account for potential ceiling effects: for chair stands, a measure of lower extremity strength, participants were asked to rise from a chair ten times as fast as possible with their arms folded across their chests (instead of five times as required in the original SPPB). The total time required to rise from the chair ten times was recorded as a continuous score. Tandem stands, used to assess postural balance skills, were extended to 30 seconds (instead of 10 seconds in the original SPBB).

With regard to the composite cognitive measure, participants completed a cognitive test battery at the 20-year assessment. Eight major areas were assessed: general verbal ability (Wechsler Adult Intelligence Scale-Revised [WAIS-R] Vocabulary and Information subtests; verbal declarative memory (Wechsler Memory Scale-Revised [WAIS-R] Verbal Paired Associates I and II; visual declarative memory (WMS-R Visual Reproduction I and II); executive function (Stroop Color-Word Test and Trail Making Test, Part B); working memory (Letter Number Span and digit span); processing speed (Trail Making Test, Part A); visual processing (Facial Recognition Test); language ability (Letter Fluency). The raw scores were converted to standardized (z) scores in the current sample, and an overall summary measure was computed (statistical methods).

Statistical Analysis

A composite neuropsychological test performance score was calculated by standardizing each cognitive test score and creating a mean z-score. We note that we also calculated a principal components analysis and found that the tests loaded on a single factor. The score derived from the factor correlated r=.92 with the composite z-score, suggesting equivalence of these two potential approaches.

We used t-tests, analysis of variance and correlational analyses to examine the associations of everyday functioning with the disability measures and regression analyses to examine the relationship of impairment indicators with residential and employment status. Regression models were used to examine the correlates of self reported disability across the two patient samples, using symptoms, everyday functioning, and the impairment indicators as predictors.

Results

The 20 year sample consisted of 233 participants (59.3% men; 78% Caucasian; 10.2% African-American). The mean age was 47.9±8.9 years. Demographics of the two diagnostic groups were not significantly different from one another apart from race (Table 1).

Table 1.

Sample Characteristics.

Schizophrenia
n=146		 Bipolar Disorder
N=87
df t
Age 47.9 8 47.6 9.6 231 .274 P=0.79
χ2 p
Sex/Male 88 (60.3%) 43 (49.5%) 2.6 0.1
Race/White* 105 (71.9%) 78 (89.7%) 13 <0.05
Residentially Independent 40 (24.7%) 60 (52.9%) 64.1 <0.001
Employed 36 (27.8%) 46 (76.7%) 39.6 <0.001
Mean ±SD Mean ±SD df t p
Schedule for the Assessment of Negative Symptoms (SANS) 28±16.3 11.6±11.6 226 5.75 <.001
Schedule for the Assessment of Positive Symptoms (SAPS) 13.25±13.6 4.2±6.5 217 6.6 <.001
Brief Psychiatric Rating Scale 34.3±10.9 25.7±7.6 222 6.5 <.001
Hamilton Depression Rating Scale (HDRS) 7.3±6 4.7±5.2 226 3.4 <.001
Neuropsychological Performance (z-Scores) −0.11±0.48 0.3±0.4 149 −5.4 <.001
Waist Circumference (in) 45.3±7.2 41.8±6.1 177 3.2 <.001
Chair Stands 0.55±0.22 0.67±0.18 153 −3.3 <.001
Balance, Scaled 0.79 0.36 0.87 0.32 169 −1.3 0.184
World Health Organization Disability Assessment Scale (WHODAS-12) 24±0 18.5±6.4 199 5 <.001
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*

Seventeen schizophrenia patients and five bipolar patients were African American (11.6 and 5.8%), 6 Asian schizophrenia patients (4.1%) and 10 and 6 were classified as unknown amongst schizophrenia and bipolar patients, respectively (0.7 % and 6.9%).

Table 1 also compares the two diagnostic groups on the various indicators of impairment. On all measures apart from balance, participants with schizophrenia had significantly greater impairment than respondents with bipolar disorder.

In order to predict employment outcomes and residential independence with the impairment indicators, we used regression models. The correlation matrix for these variables is available in Table 2. For the bipolar patients, independent living was correlated negatively with waist circumference, but no other variables. Residential independence in schizophrenia patients was correlated with negative symptom severity. In patients with bipolar disorder, full time employment was negatively correlated with all four symptom measures and waist circumference and employment was positive correlated with cognitive test performance and chair stands performance. Other than for waist circumference, the correlates of full time employment in schizophrenia patients were the same as for the bipolar patients. When examining the correlates of self reported disability, for bipolar patients, greater symptom on the SANS, HDPS, and BPRS were associated with greater self reported disability, while reduced mobility was associated with greater self reported disability. In the schizophrenia sample, self reported disability was correlated with all four symptom measures and with balance test impairments.

Table 2.

Correlations between Impairment Indicators and Employment and Residential Status

Independent
Living Status		 Employment
Status		 SAPS SANS HDRS BPRS Waist
Circumference		 Chair
Stands		 Balance Cognition
Z-Score		 WHODAS-12
Independent Living 0.2 −.05 −.17 −.07 −.1 −.3* −.01 −.02 −0.08 .14
Employment Status .25** −.26* −.33** −.35** −.30** −.27* .32* .08 .42** −.18
SAPS −.02 −.19* .22 .18 .66** .17 .16 .02 −.04 .18
SANS −.34** −.37** .14 .66** .57** .24 −.1 .17 −.34* .32*
HDRS −.11 −.16 .36** .32** .7** .044 −.12 .13 −.02 .36**
BPRS −.14 −.21* .72** .48* .61** −.21 .07 −.04 .−.13 .37*
Waist Circumference −.1 −.17 −.13 .01 .01 .05 .16* .29 .−.04 .09
Chair Stands −.08 .27** .07 −.19 −.11 .024 −.07 .16 −.3* −.40**
Balance 0.09 .012 .02 −0.91 −.91 −.15 −.29** .08 .05 −.1
Cognition z- Score .05 .22* .08 −.14 .03 −.02 −.07 .12 .06 −.27
WHODAS-12 −.12 −0.25* .29** .23* .37** .36** .17 .12 −.25* −.21
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Bipolar Disorder (grey) above the line, schizophrenia below

*

<0.01

**

<0.05

We then examined the WHODAS-12 disability total score across the two diagnostic groups, using a three-way analysis of variance examining factors of diagnosis, employment status, and residential status. Results indicated a significant main effect for diagnosis, F(1,196) = 16.69, p < .001, with schizophrenia patients reporting more disability. There was also a statistically significant effect of employment status, F(1,196)=6.23, p=.013. There was no significant effect of residential status, F(1,196)= 0.26, p=.61. There were no significant two-way or three-way interactions between the factors. Thus, residential status was not associated with WHODAS scores across the two diagnostic groups whereas members of both groups reported more disability if they were not employed.

Next, we examined the correlates of total WHODAS scores. First, we examined the two groups separately. We entered the scores on the SAPS, SANS, BPRS, HDRS, cognitive performance, balance, chair stands, and waist circumference as well as employment status and residential status. For the schizophrenia sample, the overall analysis was significant, F(2,143)=12.26, p<.001. Two variables entered the equation, BPRS scores entered first, accounting for 11% of the variance, t=4.29, p<.001, and HDRS scores entered the equation second, accounting for 4% of the variance, t=2.37, p=.02. For the bipolar patients, the overall analysis was significant, F(2,84)=8.36, p<.001. Again two variables entered the equation, HDRS scores entered first, accounting for 12% of the variance, t=3.40, p<.001, followed by chair stands, which accounted for an additional 5% of the variance, t=2.15, p=.034.

Then, to identify common predictors across the two diagnostic groups, we entered diagnosis as the first block in a regression analysis and used stepwise forward entry regression in the second block. We entered the scores on the SAPS, SANS, BPRS, HDRS, cognitive performance, balance, chair stands, and waist circumference as well as employment status and residential status. The overall analysis was significant, F(4,228)=19.42. Diagnosis accounted for 10% of the variance in total WHODAS scores, t=4.02, p<.001. Three other variables entered the equation, HDRS scores, accounting for 11% of the variance, t=5.65, p<.001, BPRS scores, accounting for 3% of the variance, t=3.02, p=.003, and waist circumference, accounting for 2% of the variance, t=2.12, p=.036. Thus, there were three variables, accounting for 16% of the variance in total WHODAS scores that were common predictors across the two diagnostic groups.

Discussion

We provide data at a 20 year follow for a well characterized sample of individuals with schizophrenia and psychotic bipolar disorder, using residential and occupational status as outcome indicators. To our knowledge, this is the longest prospective reassessment period of an incidence cohort of first-episode psychosis that has performed a wide-ranging assessment that examined multiple indicators of impairment, including self-reported disability, symptoms, cognition, and physical functioning measures to define the relationships with the two outcome domains, residential and occupational status, in schizophrenia and bipolar disorder. Twenty years after their initial hospitalization for incident psychosis, participants with psychotic bipolar disorder were more likely to be gainfully employed and living independently than participants with schizophrenia. Nonetheless, the proportion of people with both disorders who were employed and, especially, living independently 20 years after their first psychotic episode was far lower than that of population comparisons. This confirms the high individual and societal costs of schizophrenia and also highlights the considerable long-term impact of psychotic bipolar disorder.

Moreover, with a few notable exceptions, most correlations between impairment indicators and outcome were similar in bipolar disorder and schizophrenia, despite higher levels of functioning across domains in bipolar patients, in line with previous shorter-term evidence (Mausbach et al., 2010). Congruent with their higher level of functioning, bipolar patients also performed significantly better on each of the potential impairment indicators, apart from balance ability, and they also reported less overall disability than people with schizophrenia.

Further analyzing the relationships between employment and independent living status with impairment indicators in schizophrenia, employment status was associated with positive and negative symptoms, chair stand performance and waist circumference, and in bipolar disorder, by cognition, depression and waist circumference. Independence in residence was associated with negative symptoms in schizophrenia. This confirms our hypothesis that slightly different sets of impairment indicators contribute to residential and employment status in schizophrenia and bipolar disorder (Tondo et al., 2016; Bowie et al, 2010).

Negative symptoms played a significant role in achievement of both of our functional outcome measures in schizophrenia, in addition to two simple measures of physical limitations, waist circumference and the ability to repeatedly rise from a chair. The association between cognition and vocational outcome in bipolar disorders has been noted before (Bowie et al., 2010), consistent with our observations. In contrast, physical performance measures, even if as simple as chair stands, while commonly used to in geriatric populations, have rarely been used to characterize functioning in epidemiological studies in the adult mental health field, but merit further consideration for their apparent impact on functioning. The recent suggestion of ‘exaggerated aging’ taking place in schizophrenia and perhaps in bipolar disorder, may further highlight the need for physical performance assessments to take place, just like it is customarily done in healthy aging populations (Harvey & Rosenthal, 2017). The association of symptoms with objective outcome in bipolar disorder was confined to depression, also confirming prior reports (Bowie et al., 2010). While negative symptoms are long established determinants of outcome in schizophrenia, they are not as often measured in bipolar disorder and are considered less of a core determinant of bipolar disorder (Atkinson et al., 1997).

WHODAS-12 self-reported disability was not associated with residential status in either schizophrenia or bipolar disorder but was associated with employment status in schizophrenia. Interestingly, symptoms were more strongly correlated with total scores on the self-reported WHODAS than other impairment indicators in both groups. This is likely because the experience of symptoms can influence self-reports, consistent with previous findings (Sabbag et al., 2012; Atkinson et al. 1997; Gould et al., 2013). The regression analysis suggested that global psychopathology, depression, and waist circumference were predictors of self-assessed disability across the two patient groups. Thus, controlling for diagnosis suggests a commonality in the two groups of referencing subjective disability in terms of psychopathology and physical functioning.

In a completely separate sample, we (Harvey et al., 2017) found that depression in patients with schizophrenia was associated with subjective reports of impairment in everyday functioning. In that study, like the present one, depression was not associated with objectively defined impairments in everyday functioning or performance-based assessments of cognition or the ability to perform everyday functional skills.

In drawing inferences, it is important to be cognizant of the study’s limitations. The current system of disability payments in the United States may make it difficult to interpret functioning as related to job status (Davidson et al., 2016). Disability status, once granted, links the individual to multiple services including health care. Returning to work may reduce or eliminate benefits, creating a disincentive to engaging in compensated employment. Residential independence may be challenging to predict. The majority of participants with schizophrenia were also unemployed. Chronic unemployment, has the potential to lead to chronic residential problems, particularly in an area such as Suffolk County with a high cost-of-living compared to the national average. Similarly, underemployment may exert an influence both disorders: while characterized in the sample as gainfully employed, participants may not be able to afford to live independently as compared to other, less high-cost areas and instead continue to live with their family out of economic necessity.

Conclusions

Impairment indicators including physical functioning were differentially associated with employment and residential status in bipolar disorder and schizophrenia, with bipolar disorder representing the less impaired group. Self reports of functioning were not related to residential independence, underscoring the need for performance-based assessment of everyday activities. Moreover, people with schizophrenia and bipolar disorder may perceive disability in terms of symptom severity and physical limitations more than in terms of cognitive deficits. Treatments aimed at physical fitness may have the potential to improve both objective functioning and subjective quality of life in people with schizophrenia and bipolar disorder.

Acknowledgments

The authors gratefully acknowledge the ongoing support of the participants and mental health community of Suffolk County, the consensus psychiatrist team, and the study interviewers and coordinators, with special thanks to Janet Lavelle.

Funding Source

This research was supported by grants from the National Institutes of Health (MH44801 to EJB and MH094398 to RK), Eli Lilly Corporation (to EJB), The Stanley Medical Research Institute (to EJB) and Stony Brook University’s Clinical Research Scholar Award (to RK).

Footnotes

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Conflict of Interest

Over the past 12 months, Dr. Harvey has served as a consultant to: Allergan, Akili, Boehringer-Ingelheim, Lundbeck, Otsuka Digital Health, Sanofi, Takeda. He receives royalties from Neurocog Trials and has research grants from Sunovion, Takeda and the Stanley Medical Research Foundation. Dr. Strassnig is a shareholder of Johnson & Johnson.

Contributors

Drs. Strassnig, Harvey and Kalin analyzed the data and wrote the manuscript. Drs. Kotov, Fochtmann and Bromet collected the data and wrote the manuscript.

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