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Item response theory-based measure of global disability in multiple sclerosis derived from the Performance Scales and related items.

Chamot E, Kister I, Cutter GR - BMC Neurol (2014)

Bottom Line: The construct validity of the three scores was compared by examining the magnitude of their associations with participant's background characteristics, including unemployment.We derived structurally valid measures of global disability from the PS through the proposed methodology that were superior to the PSS.Higher scores of global disability were significantly associated with older age at assessment, longer disease duration, male gender, Native-American ethnicity, not receiving disease modifying therapy, unemployment, and higher scores on the Patient Determined Disease Steps (PDDS).

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology, University of Alabama at Birmingham School of Public Health, 1665 University Blvd, Suite 217H, Birmingham 35294-0022, AL, USA. echamot@uab.edu.

ABSTRACT

Background: The eight Performance Scales and three assimilated scales (PS) used in North American Research Committee on Multiple Sclerosis (NARCOMS) registry surveys cover a broad range of neurologic domains commonly affected by multiple sclerosis (mobility, hand function, vision, fatigue, cognition, bladder/bowel, sensory, spasticity, pain, depression, and tremor/coordination). Each scale consists of a single 6-to-7-point Likert item with response categories ranging from "normal" to "total disability". Relatively little is known about the performances of the summary index of disability derived from these scales (the Performance Scales Sum or PSS). In this study, we demonstrate the value of a combination of classical and modern methods recently proposed by the Patient-Reported Outcome Measurement Information System (PROMIS) network to evaluate the psychometric properties of the PSS and derive an improved measure of global disability from the PS.

Methods: The study sample included 7,851adults with MS who completed a NARCOMS intake questionnaire between 2003 and 2011. Factor analysis, bifactor modeling, and item response theory (IRT) analysis were used to evaluate the dimension(s) of disability underlying the PS; calibrate the 11 scales; and generate three alternative summary scores of global disability corresponding to different model assumptions and practical priorities. The construct validity of the three scores was compared by examining the magnitude of their associations with participant's background characteristics, including unemployment.

Results: We derived structurally valid measures of global disability from the PS through the proposed methodology that were superior to the PSS. The measure most applicable to clinical practice gives similar weight to physical and mental disability. Overall reliability of the new measure is acceptable for individual comparisons (0.87). Higher scores of global disability were significantly associated with older age at assessment, longer disease duration, male gender, Native-American ethnicity, not receiving disease modifying therapy, unemployment, and higher scores on the Patient Determined Disease Steps (PDDS).

Conclusion: Promising, interpretable and easily-obtainable IRT scores of global disability were generated from the PS by using a sequence of traditional and modern psychometric methods based on PROMIS recommendations. Our analyses shed new light on the construct of global disability in MS.

No MeSH data available.


Related in: MedlinePlus

Associations between Performance Scales-based, IRT-derived, scores of disability and PDDS scores in a sample of NARCOMS registrants. a) Scores of global disability generated from the bifactor IRT model (●) versus the unidimensional IRT model (□, pattern scores; ▲, summed scores). b) Scores of residual physical disability generated from the bifactor IRT model. c) Scores of residual mental disability generated from the bifactor IRT model. Note: Although the scores of global disability, residual physical disability, and residual mental disability are all reported as scaled scores (Mean, 50; SD, 15), they are not on the same metric. Error bars represent 95% confidence intervals. Spearman correlations between IRT scores and PDDS scores: Figure 5a) ● 0.60, □ 0.65, ▲0.68; Figure 5b) 0.72; Figure 5c) 0.07.
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Fig5: Associations between Performance Scales-based, IRT-derived, scores of disability and PDDS scores in a sample of NARCOMS registrants. a) Scores of global disability generated from the bifactor IRT model (●) versus the unidimensional IRT model (□, pattern scores; ▲, summed scores). b) Scores of residual physical disability generated from the bifactor IRT model. c) Scores of residual mental disability generated from the bifactor IRT model. Note: Although the scores of global disability, residual physical disability, and residual mental disability are all reported as scaled scores (Mean, 50; SD, 15), they are not on the same metric. Error bars represent 95% confidence intervals. Spearman correlations between IRT scores and PDDS scores: Figure 5a) ● 0.60, □ 0.65, ▲0.68; Figure 5b) 0.72; Figure 5c) 0.07.

Mentions: We observed positive and statistically significant associations between mean IRT scores of global disability and PDDS scores (P < 0.001; Figure 5A). Increases in IRT scores of global disability were sharper over the lower portion of the PDSS scale (0-to-2) than over its higher portion (3-to-8). Differences between summed-, pattern- , and bifactor score estimates of global disability were generally minimal (standardized differences <0.15 except for PDDS 7). Mean bifactor scores of residual physical disability increased significantly and nearly linearly with increasing PDSS scores (P < 0.001; Figure 5B). In contrast, mean bifactor scores of residual mental disability increased significantly over PDSS scores 0-to-2 and then decreased (Figure 5C). The patterns in Figure 5 are consistent with the higher portion of the PDDS scale being biased toward physical disability. Alternatively, these patterns may also indicate that patients experiencing high levels of “mental” disability were less likely to enroll in NARCOMS.Figure 5


Item response theory-based measure of global disability in multiple sclerosis derived from the Performance Scales and related items.

Chamot E, Kister I, Cutter GR - BMC Neurol (2014)

Associations between Performance Scales-based, IRT-derived, scores of disability and PDDS scores in a sample of NARCOMS registrants. a) Scores of global disability generated from the bifactor IRT model (●) versus the unidimensional IRT model (□, pattern scores; ▲, summed scores). b) Scores of residual physical disability generated from the bifactor IRT model. c) Scores of residual mental disability generated from the bifactor IRT model. Note: Although the scores of global disability, residual physical disability, and residual mental disability are all reported as scaled scores (Mean, 50; SD, 15), they are not on the same metric. Error bars represent 95% confidence intervals. Spearman correlations between IRT scores and PDDS scores: Figure 5a) ● 0.60, □ 0.65, ▲0.68; Figure 5b) 0.72; Figure 5c) 0.07.
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Related In: Results  -  Collection

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Fig5: Associations between Performance Scales-based, IRT-derived, scores of disability and PDDS scores in a sample of NARCOMS registrants. a) Scores of global disability generated from the bifactor IRT model (●) versus the unidimensional IRT model (□, pattern scores; ▲, summed scores). b) Scores of residual physical disability generated from the bifactor IRT model. c) Scores of residual mental disability generated from the bifactor IRT model. Note: Although the scores of global disability, residual physical disability, and residual mental disability are all reported as scaled scores (Mean, 50; SD, 15), they are not on the same metric. Error bars represent 95% confidence intervals. Spearman correlations between IRT scores and PDDS scores: Figure 5a) ● 0.60, □ 0.65, ▲0.68; Figure 5b) 0.72; Figure 5c) 0.07.
Mentions: We observed positive and statistically significant associations between mean IRT scores of global disability and PDDS scores (P < 0.001; Figure 5A). Increases in IRT scores of global disability were sharper over the lower portion of the PDSS scale (0-to-2) than over its higher portion (3-to-8). Differences between summed-, pattern- , and bifactor score estimates of global disability were generally minimal (standardized differences <0.15 except for PDDS 7). Mean bifactor scores of residual physical disability increased significantly and nearly linearly with increasing PDSS scores (P < 0.001; Figure 5B). In contrast, mean bifactor scores of residual mental disability increased significantly over PDSS scores 0-to-2 and then decreased (Figure 5C). The patterns in Figure 5 are consistent with the higher portion of the PDDS scale being biased toward physical disability. Alternatively, these patterns may also indicate that patients experiencing high levels of “mental” disability were less likely to enroll in NARCOMS.Figure 5

Bottom Line: The construct validity of the three scores was compared by examining the magnitude of their associations with participant's background characteristics, including unemployment.We derived structurally valid measures of global disability from the PS through the proposed methodology that were superior to the PSS.Higher scores of global disability were significantly associated with older age at assessment, longer disease duration, male gender, Native-American ethnicity, not receiving disease modifying therapy, unemployment, and higher scores on the Patient Determined Disease Steps (PDDS).

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology, University of Alabama at Birmingham School of Public Health, 1665 University Blvd, Suite 217H, Birmingham 35294-0022, AL, USA. echamot@uab.edu.

ABSTRACT

Background: The eight Performance Scales and three assimilated scales (PS) used in North American Research Committee on Multiple Sclerosis (NARCOMS) registry surveys cover a broad range of neurologic domains commonly affected by multiple sclerosis (mobility, hand function, vision, fatigue, cognition, bladder/bowel, sensory, spasticity, pain, depression, and tremor/coordination). Each scale consists of a single 6-to-7-point Likert item with response categories ranging from "normal" to "total disability". Relatively little is known about the performances of the summary index of disability derived from these scales (the Performance Scales Sum or PSS). In this study, we demonstrate the value of a combination of classical and modern methods recently proposed by the Patient-Reported Outcome Measurement Information System (PROMIS) network to evaluate the psychometric properties of the PSS and derive an improved measure of global disability from the PS.

Methods: The study sample included 7,851adults with MS who completed a NARCOMS intake questionnaire between 2003 and 2011. Factor analysis, bifactor modeling, and item response theory (IRT) analysis were used to evaluate the dimension(s) of disability underlying the PS; calibrate the 11 scales; and generate three alternative summary scores of global disability corresponding to different model assumptions and practical priorities. The construct validity of the three scores was compared by examining the magnitude of their associations with participant's background characteristics, including unemployment.

Results: We derived structurally valid measures of global disability from the PS through the proposed methodology that were superior to the PSS. The measure most applicable to clinical practice gives similar weight to physical and mental disability. Overall reliability of the new measure is acceptable for individual comparisons (0.87). Higher scores of global disability were significantly associated with older age at assessment, longer disease duration, male gender, Native-American ethnicity, not receiving disease modifying therapy, unemployment, and higher scores on the Patient Determined Disease Steps (PDDS).

Conclusion: Promising, interpretable and easily-obtainable IRT scores of global disability were generated from the PS by using a sequence of traditional and modern psychometric methods based on PROMIS recommendations. Our analyses shed new light on the construct of global disability in MS.

No MeSH data available.


Related in: MedlinePlus