Abstract
Objective
Gastrointestinal (GI) involvement is common in patients with systemic sclerosis (SSc). The Patient-Reported Outcomes Measurement Information System (PROMIS®) GI Symptom item bank captures upper and lower GI symptoms (reflux, disrupted swallowing, nausea/vomiting, belly pain, gas /bloating /flatulence, diarrhea, constipation, and fecal incontinence). The objective of this study was to evaluate the construct validity of the PROMIS-GI bank in SSc.
Methods
167 patients with SSc were administered the PROMIS GI bank and the UCLA Scleroderma Clinical Trials Consortium Gastrointestinal Scale (GIT 2.0) instrument. GIT 2.0 is a multi-item instrument that measures SSc-associated GI symptoms. Product-moment correlations and a multitrait-multimethod analysis of the PROMIS GI scales with the GIT 2.0 symptom scales were used to evaluate convergent and discriminant validity.
Results
Patients with SSc GI involvement had PROMIS GI scale scores 0.2–0.7 SD worse than US population. Correlations among scales measuring the same domains for the PROMIS GI and GIT 2.0 measures were large, ranging from 0.61 to 0.87 (average r = 0.77). The average correlation between different symptom scales was 0.22, supporting discriminant validity.
Conclusion
This study provides support for the construct validity of the PROMIS GI scales in SSc. Future research is needed to assess the responsiveness to change of these scales in patients with SSc.
INTRODUCTION
Patient-reported outcomes (PROs) are widely used in research and they are playing an increasingly important role in clinical practice (1). In a clinical practice, PROs can be administered to identify presence/ absence of symptoms or assess symptoms severity which can assist in clinical decision making (2). Unlike the traditional measures of disease burden (direct and indirect expenditures of a disease), PRO instruments document the burden of disease in terms of impact on daily functioning and well-being, or health-related quality of life (HRQOL) (3).
Gastrointestinal tract (GI) involvement occurs in approximately 90% of patients with systemic sclerosis (SSc) (4, 5) and is associated with decline in HRQOL (6, 7). The University of California, Los Angeles Scleroderma Clinical Trials Consortium Gastrointestinal Scale (UCLA SCTC GIT 2.0; GIT 2.0 from hereon) is a multi-item instrument that measures GI symptoms and their impact on HRQOL. Support for the reliability and validity (including responsiveness to change) of the GIT 2.0 was found in different observational cohorts (8–11). It is considered the “legacy” instrument to assess GI involvement in patients with SSc (2).
The National Institutes of Health (NIH)-funded the Patient-Reported Outcomes Measurement Information System (PROMIS®) Roadmap to develop, evaluate, and standardize item banks to measure patient-reported outcomes across patients with different medical conditions and in the US general population (12, 13). PROMIS GI Symptom item banks that assess 8 GI domains were recently developed (14, 15). The goal of PROMIS is to develop reliable and valid item banks using item response theory (IRT) that can be administered in a variety of formats including short forms and computerized adaptive tests (12, 16, 17). PROMIS has several advantages over the traditional instruments. First, a consistent qualitative process is employed with detailed systematic review, focus groups, cognitive interviews, and translatability for each item bank. Second, PROMIS static items produce more reliable information than existing measures such as the SF-36 physical functioning-10 and health assessment questionnaire-disability index (18).
The goal of this study was to evaluate the construct validity of the PROMIS GI Symptom scales.
MATERIALS AND METHODS
Patient-reported outcome measures
NIH PROMIS GI Symptom item bank
The GI Symptom item banks were developed using the standard PROMIS qualitative and quantitative methodology (19). Briefly, the qualitative aim was achieved through completion of a systematic review of the literature to identify extant GI PRO items followed by a comprehensive review and evaluation of these items (15). The individual items from existing instruments were grouped based on different symptoms. This was complemented by focus group discussions of patients with GI conditions to evaluate their symptoms. New items were developed based on extant items and input from the focus group participants followed by fine tuning of item wording based on cognitive interviews with GI patients. The items were administered to 865 patients with different GI disorders (including SSc) at 4 centers in United States: University of Michigan Hospital, University of California Los Angeles Medical Center, Cedars Sinai Medical Center and VA West Los Angeles Medical Center and 1,177 individuals from the US general population. The US general population was included to develop norms for clinical care and research. Items were finalized based on psychometric analyses including categorical confirmatory factor analyses and item response theory modeling (15).
The final PROMIS GI Symptom instrument (15) has 60 items and assesses 8 domains: gastroesophageal reflux (13 items), disrupted swallowing (7 items), diarrhea (5 items), bowel incontinence/soilage (4 items), nausea and vomiting (4 items), constipation (9 items), belly pain (6 items), and gas /bloating /flatulence (12 items). All scales were calibrated using the two-parameter item response theory (IRT) graded response model and scored on a T-score metric with a mean of 50 and SD of 10 in the U.S. general population. A higher score denotes more GI symptoms. The recall period for PROMIS GI Symptom items is 1-week.
GIT 2.0
The GIT 2.0 was developed to assess presence / absence and severity of gastrointestinal involvement and the consequent impairment in social and emotional well-being in patients with SSc (11). Previous work has provided support for the reliability and validity of the GIT 2.0 scales (11, 20). The GIT 2.0 scales were found to be sensitive to the presence of abnormalities on structural / motility testing and can be routinely used as initial screening test in clinical practice (8). It is the “legacy” PRO measure to assess the severity of GI involvement and its impact on HRQOL in patients with SSc. The GIT 2.0 has 34 items; the 7 multi-item scales include reflux (8 items), distention/bloating (4 items), diarrhea (2 items), fecal soilage (1 item), constipation (4 items), emotional well-being (9 items), and social functioning (6 items) (2). The reflux scale has 1 item each for solid food dysphagia, nausea and vomiting. The items are scored from 0.0–3.0, except diarrhea (0.0–2.0) and constipation (0.0–2.5). Higher values indicate worse HRQOL. The total GIT 2.0 score averages 6 of 7 scales (excluding constipation) and is scored from 0.0 (no GI symptoms) to 2.8 (severe GI symptoms). The recall period for the GIT 2.0 items is 1-week.
Participants
167 patients with SSc are a subset of 865 patients who were recruited predominantly at the University of Michigan scleroderma clinic. The diagnosis of SSc was made based on the 1980 American College of Rheumatology criteria (21) and / or clinical diagnosis by PPK or DK. This subset of patients were administered the PROMIS GI Symptom item bank and GIT 2.0 instrument.
Statistical analysis
Descriptive statistics are presented as mean (standard deviations) for continuous variables and percentages for categorical variables. In addition to mean scores and standard deviations (SD), ranges, and percentages of respondents scoring the minimum and maximum possible scores were calculated to evaluate scale score distributions for the PROMIS GI Symptom and GIT 2.0 scales. Internal consistency reliability for all scales was estimated using Cronbach’s alpha and reliability for the GIT 2.0 total score was estimated using Mosier’s formula. Reliability ≥ 0.70 was considered satisfactory for group comparisons (22).
Convergent and discriminant validity are two components of construct validity. Convergent validity is supported when different methods of assessing the same construct (e.g. two measures of reflux) should be highly correlated. Pearson’s product-moment correlations of the PROMIS GI Symptom scales with corresponding GIT 2.0 scales were used to assess convergent validity. Discriminant validity is supported when measures of different constructs (e.g. diarrhea and constipation) do not correlate highly with each other. We conducted multitrait-multimethod Matrix (MTMM) analyses to evaluate convergent and discriminant validity (23). We hypothesized that correlations among scales measuring the same construct would be significantly larger than other correlations (24). A coefficient of ≥ 0.50 was considered large for current analysis.
RESULTS
The majority of participants were female (91%), Caucasian (54%), and highly educated (98% with some college degree); the mean age of the sample was 53 years (SD = 13; Table 1).
Table 1.
describes the baseline characteristics of the study participants
| Variables | Total sample (n=167) |
|---|---|
| Age in years, Mean (range), SD | 53 (22–80), SD = 13 |
| Women (%) | 91% |
| Race / Ethnicity | |
| White | 67% |
| African American | 11% |
| Hispanic | 10% |
| Asian | 7% |
| Other | 5% |
| Education | |
| Less than or equal to college education | 2% |
| Some college | 16% |
| College graduate | 20% |
| Graduate degree | 63% |
| Marital status | |
| Married | 65% |
| Never married | 10% |
| Widowed / separated / divorced | 25% |
| Employment | |
| Employed full-time/part-time | 38% |
| Retired | 24% |
| Unemployed | 4% |
| On disability | 22% |
| Homemakers | 10% |
| Full-time student | 2% |
Table 2 provides descriptive statistics and reliability estimates for the PROMIS GI Symptom and GIT 2.0 scales. Patients in the sample had PROMIS GI scale scores 0.2–0.7 SD worse than the US population. The percentage of patients with minimum scores on the PROMIS scales ranged from 1% (for reflux, bloating and diarrhea scales) to 47% (for fecal incontinence scale) while the percentage with maximum scores was 1% for all scales. Cronbach’s coefficient alpha was >0.70 for all scales.
Table 2.
Descriptive statistics of PROMIS GI item bank and GIT 2.0
| Scale | Mean (SD) | Minimum score | Maximum score | % with minimum | % with maximum | Cronbach’s α |
|---|---|---|---|---|---|---|
| PROMIS GI Symptom item bank | ||||||
| Reflux | 54 (8) | 33 | 75 | 1 | 1 | 0.83 |
| Disrupted swallowing | 56 (10) | 41 | 83 | 14 | 1 | 0.91 |
| Nausea/ vomiting | 54 (11) | 41 | 84 | 20 | 1 | 0.73 |
| Belly pain | 55 (10) | 37 | 79 | 2 | 1 | 0.88 |
| Gas / bloat / flatulence | 57 (10) | 38 | 79 | 1 | 1 | 0.94 |
| Diarrhea | 55 (11) | 40 | 82 | 1 | 1 | 0.89 |
| Constipation | 52 (9) | 37 | 75 | 7 | 1 | 0.88 |
| Fecal incontinence | 54 (13) | 44 | 91 | 47 | 1 | 0.90 |
|
| ||||||
| UCLA SCTC GIT 2.0 | ||||||
| Reflux | 0.85 (0.63) | 0.0 | 3.0 | 8 | 1 | 0.80 |
| Distention / bloating | 1.38 (0.87) | 0.0 | 3.0 | 4 | 6 | 0.78 |
| Diarrhea | 0.65 (0.70) | 0.0 | 2.0 | 45 | 9 | 0.72 |
| Fecal soilage | 0.47 (0.81) | 0.0 | 3.0 | 69 | 4 | N/A |
| Constipation | 0.61 (0.59) | 0.0 | 2.5 | 26 | 1 | 0.74 |
| Emotional well-being | 0.66 (0.74) | 0.0 | 3.0 | 27 | 1 | 0.90 |
| Social functioning | 0.52 (0.58) | 0.0 | 2.33 | 34 | 1 | 0.78 |
| Total GI score | 0.75 (0.51) | 0.0 | 2.34 | 1 | 0 | 0.92 |
For GIT 2.0, the mean (SD) scores ranged from 0.47 (0.81) for fecal soilage to 1.38 (0.87) for distension/ bloating scale. The percentage of patients with minimum scores ranged from 4% (for distension / bloating scale) to 69% (for fecal soilage scale) while the percentage with maximum scores ranged from 1% (for reflux, constipation, emotional well-being and social functioning scales) to 9% (for diarrhea scale). Cronbach’s alpha was >0.70 for all scales.
Pearson’s product-moment correlations between corresponding scale scores were large (ranging from 0.61 to 0.87) (Table 3). GIT 2.0 does not have separate scales for disrupted swallowing and nausea / vomiting. However, the GIT 2.0 reflux scale has a single item assessing solid food dysphagia, and nausea and vomiting items. This accounts for the relatively high correlations of the reflux, disrupted swallowing and nausea/vomiting scales on the PROMIS GI Symptom scales with the GIT 2.0 reflux scale.
Table 3.
Product-moment correlations between PROMIS GI Symptom item bank and UCLA SCTC GIT 2.0 symptom scales
| UCLA SCTC GIT 2.0 | ||||||
|---|---|---|---|---|---|---|
|
| ||||||
| Reflux* | Distention/ bloating, | Diarrhea | Constipation | Fecal incontinence | ||
| PROMIS GI | Reflux | 0.77 | 0.44 | 0.13 | 0.25 | −0.03 |
| Disrupted swallowing | 0.61 | 0.39 | 0.16 | 0.21 | 0.13 | |
| Nausea and vomiting | 0.66 | 0.44 | 0.20 | 0.22 | 0.18 | |
| Belly pain | 0.45 | 0.49 | 0.23 | 0.34 | 0.04 | |
| Gas/ bloat/ flatulence | 0.46 | 0.73 | 0.30 | 0.29 | 0.10 | |
| Diarrhea | 0.25 | 0.25 | 0.65 | 0.02 | 0.54 | |
| Constipation | 0.37 | 0.32 | 0.05 | 0.76 | −0.01 | |
| Fecal incontinence | 0.12 | 0.11 | 0.43 | −0.18 | 0.87 | |
GIT 2.0 Reflux scale asks about reflux, dysphagia to solid foods, and nausea/ vomiting. Bold represents hypothesized correlation coefficients.
The average convergent validity correlation in the MTMM was 0.77 and the average off-diagonal correlation was 0.22 (Table 4). T-tests of the significance of differences between relevant corresponding correlations for evaluating discriminant validity showed that 39 out of 40 hetero-method (convergent correlations compared with correlations among different constructs measured by different methods) and 39 out of 40 mono-method (convergent correlations compared with correlations among the different constructs measured by the same method) comparisons were statistically significant in the hypothesized direction, providing strong support for construct validity.
Table 4.
Multitrait-Multimethod Matrix (MTMM) table of correlations
| Method Trait | GIT 2.0 | PROMIS-GI | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Reflux | Gas | Diarrhea | Constipation | Incontinence | Reflux | Gas | Diarrhea | Constipation | ||
| GIT 2.0 | Reflux | 1.00 | ||||||||
| Gas | 0.57 | 1.00 | ||||||||
| Diarrhea | 0.13 | 0.23 | 1.00 | |||||||
| Constipation | 0.34 | 0.22 | −0.14 | 1.00 | ||||||
| Incontinence | 0.10 | 0.14 | 0.38 | −0.12 | 1.00 | |||||
|
| ||||||||||
| PROMIS-GI | Reflux | [0.77] | 0.44 | 0.13 | 0.25 | −0.03 | 1.00 | |||
| Gas | 0.46 | [0.73] | 0.30 | 0.29 | 0.10 | 0.39 | 1.00 | |||
| Diarrhea | 0.25 | 0.25 | [0.65] | 0.02 | 0.54 | 0.23 | 0.31 | 1.00 | ||
| Constipation | 0.37 | 0.32 | 0.05 | [0.76] | −0.01 | 0.35 | 0.36 | 0.20 | 1.00 | |
| Incontinence | 0.12 | 0.11 | 0.43 | −0.18 | [0.87] | 0.06 | 0.11 | 0.61 | −0.06 | |
N = 167; DFS = 164
Average convergent validity correlation is 0.766
Average off-diagonal correlation is 0.225
DISCUSSION
GI involvement affects approximately 90% of SSc patients (25) and majority of patients have symptoms. Although the preferred approach for evaluation of GI pathology is tests such as endoscopy and manometry, it is impractical to perform these tests in every patient, particularly as symptoms evolve over time (2). PRO measures complement objective tests (8) and GI symptoms in SSc are independently associated with poor HRQOL (26).
The PROMIS GI scales assess symptoms that can be used to assess the general population and patients with different GI disorders. In the current study, PROMIS GI Symptom scales were compared to the widely used GIT 2.0 to explore its construct validity in patients with SSc. Correlations between PROMIS GI scales and corresponding GIT 2.0 scales were large and correlations of scales measuring different constructs were small, providing support for construct validity.
The largest correlation between PROMIS GI scales and corresponding GIT 2.0 scales was for fecal incontinence (r = 0.87) and this may be attributed to a single item that is worded very similarly to GIT 2.0. A high correlation was also noted between the PROMIS reflux, disrupted swallowing and nausea/vomiting scales and the GIT 2.0 reflux scale (r= 0.77, 0.61 and 0.66, respectively). This is likely, as the GIT 2.0 does not have separate scales for disrupted swallowing and nausea and vomiting; the reflux scale of GIT 2.0 includes an item each for solid food dysphagia, nausea, and vomiting. Solid and liquid dysphagia and nausea/ vomiting are common in patients in SSc due to GERD, esophageal dysmotility and gastroparesis (25, 27–29). Hence, separate scales for disrupted swallowing and nausea/vomiting are more meaningful in patients with SSc. The correlations between diarrhea and fecal incontinence scales for the 2 instruments were also noteworthy (range 0.43 to 0.54). During our qualitative phase for development of PROMIS GI scale, some patients stated that loose / frequent bowel movements and fecal incontinence were in a continuum rather than separate constructs. This is also supported by negative correlations between fecal incontinence and constipation scales (range −0.01 to −0.18).
PROMIS GI scales and GIT 2.0 demonstrated satisfactory reliability (> 0.70 for all scales). The percentage of patients with minimum and maximum scores can limit responsiveness to change in a longitudinal study. In our study, PROMIS scales had lower percentage of patients in different scales who achieved minimum and maximum scores compared to GIT 2.0 suggesting that measurement precision may be better for PROMIS bank over a wide range compared to GIT 2.0. This will likely increase the ability to detect true change and to fulfill power and sample size requirements (30, 31).
Our study has several strengths. First, it provides support for the PROMIS GI Symptom scales in patients with SSc. Next, it adds to the limited repertoire of psychometrically sound instruments to assess the GI burden of SSc. In clinical practice and trials, incorporation of either GIT 2.0 or PROMIS GI scales is appropriate. Third, PROMIS GI has advantage of separate scales for disrupted swallowing and nausea/ vomiting (applicable in SSc) and will have data available on same metric that allows comparison of prevalence/ severity of symptoms in patients with SSc with general population and other GI disorders such as inflammatory bowel disease and irritable bowel disorder. On the other hand, PROMIS GI scales require a computer to calculate the scores whereas GIT 2.0 can be scored in the office setting.
The study is not without limitations. First, the GIT 2.0 was one of the “legacy” instruments used during the development of GI Symptom item bank. Although there are other measures to assess GI involvement in SSc, none have been comprehensivly evaluated as GIT 2.0 (2). Second, the study population was quite homogenous predominantly involving females (91%), mainly Caucasians and patients who were highly educated (63% with graduate degree). Larger studies in SSc and other GI disorders will need to be conducted to assess responsiveness to change of PROMIS GI item bank vs. other “legacy” instruments.
In conclusion, this study provides support for the construct validity of the PROMIS GI Symptom item scales in patients with SSc. These items are ready for use in clinical practice to assess the presence and severity of GI symptoms.
Significance and innovations.
Patient reported outcomes (PRO) play an important role in clinical practice. They help to assess the disease burden and guide treatment.
PROMIS instruments are more precise than existing legacy measures.
Newly developed PROMIS GI Symptom item bank captures 8 GI-specific symptom scales for luminal GI disorders.
In patients with SSc, PROMIS GI scales showed construct (convergent and discriminant) validity relative to a legacy instrument (UCLA Scleroderma Clinical Trials Consortium Gastrointestinal scale [GIT 2.0]).
Compared to GIT 2.0, PROMIS GI bank has additional scales that are applicable to patients with SSc.
Acknowledgments
Grant support: The research reported in this publication was supported by NIH/NIAMS U01 AR057936A, the National Institutes of Health through the NIH Roadmap for Medical Research Grant (AR052177) The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Dinesh Khanna was also supported by the NIH/NIAMS K24AR063120-02. Ron D. Hays was supported by NIH/NIA Grants P30-AG028748 and P30-AG021684, and NCMHD Grant 2P20MD000182.
PROMIS® was funded with cooperative agreements from the National Institutes of Health (NIH) Common Fund Initiative (Northwestern University, PI: David Cella, PhD, U54AR057951, U01AR052177; Northwestern University, PI: Richard C. Gershon, PhD, U54AR057943; American Institutes for Research, PI: Susan (San) D. Keller, PhD, U54AR057926; State University of New York, Stony Brook, PIs: Joan E. Broderick, PhD and Arthur A. Stone, PhD, U01AR057948, U01AR052170; University of Washington, Seattle, PIs: Heidi M. Crane, MD, MPH, Paul K. Crane, MD, MPH, and Donald L. Patrick, PhD, U01AR057954; University of Washington, Seattle, PI: Dagmar Amtmann, PhD, U01AR052171; University of North Carolina, Chapel Hill, PI: Harry A. Guess, MD, PhD (deceased), Darren A. DeWalt, MD, MPH, U01AR052181; Children’s Hospital of Philadelphia, PI: Christopher B. Forrest, MD, PhD, U01AR057956; Stanford University, PI: James F. Fries, MD, U01AR052158; Boston University, PIs: Alan Jette, PT, PhD, Stephen M. Haley, PhD (deceased), and David Scott Tulsky, PhD (University of Michigan, Ann Arbor), U01AR057929; University of California, Los Angeles, PIs: Dinesh Khanna, MD (University of Michigan, Ann Arbor) and Brennan Spiegel, MD, MSHS, U01AR057936; University of Pittsburgh, PI: Paul A. Pilkonis, PhD, U01AR052155; Georgetown University, PIs: Carol. M. Moinpour, PhD (Fred Hutchinson Cancer Research Center, Seattle) and Arnold L. Potosky, PhD, U01AR057971; Children’s Hospital Medical Center, Cincinnati, PI: Esi M. Morgan DeWitt, MD, MSCE, U01AR057940; University of Maryland, Baltimore, PI: Lisa M. Shulman, MD, U01AR057967; and Duke University, PI: Kevin P. Weinfurt, PhD, U01AR052186). NIH Science Officers on this project have included Deborah Ader, PhD, Vanessa Ameen, MD (deceased), Susan Czajkowski, PhD, Basil Eldadah, MD, PhD, Lawrence Fine, MD, DrPH, Lawrence Fox, MD, PhD, Lynne Haverkos, MD, MPH, Thomas Hilton, PhD, Laura Lee Johnson, PhD, Michael Kozak, PhD, Peter Lyster, PhD, Donald Mattison, MD, Claudia Moy, PhD, Louis Quatrano, PhD, Bryce Reeve, PhD, William Riley, PhD, Peter Scheidt, MD, Ashley Wilder Smith, PhD, MPH, Susana Serrate-Sztein, MD, William Phillip Tonkins, DrPH, Ellen Werner, PhD, Tisha Wiley, PhD, and James Witter, MD, PhD. The contents of this article uses data developed under PROMIS. These contents do not necessarily represent an endorsement by the US Federal Government or PROMIS. See http://www.nihpromis.org for additional information on the PROMIS® initiative.
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