Measuring upper limb capacity in poststroke patients: development, fit of the monotone homogeneity model, unidimensionality, fit of the double monotonicity model, differential item functioning, internal consistency, and feasibility of the stroke upper limb capacity scale, SULCS.
Subject: Measuring instruments (Analysis)
Measuring instruments (Measurement)
Stroke patients (Analysis)
Stroke patients (Measurement)
Authors: Roorda, L.D.
Houwink, A.
Smits, W.
Molenaar, I.W.
Geurts, A.C.
Pub Date: 07/01/2011
Publication: Name: New Zealand Journal of Physiotherapy Publisher: New Zealand Society of Physiotherapists Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2011 New Zealand Society of Physiotherapists ISSN: 0303-7193
Issue: Date: July, 2011 Source Volume: 39 Source Issue: 2
Product: Product Code: 3820001 Mechanical Measuring Equip NAICS Code: 334519 Other Measuring and Controlling Device Manufacturing
Accession Number: 288537993
Full Text: Aims

To develop an assessment tool for upper limb capacity as defined by the International Classification of Function, Disability and Health (ICF). The assessment tool was intended to be quick and easy to use, able to assess basic and advanced upper limb function, and not require specialised equipment. The authors also sought to test some psychometric properties of the Stroke Upper Limb Capacity Scale (SULCS) assessment tool.

Method

The SULCS instrument was developed after extensive consultation with rehabilitation experts, and after two pilot studies. The initial instrument consisted of fifteen test items with a response option of either 0 (unable to perform the task) or 1 (able to perform the task). This cohort study involved 400 participants (group 1A) with a diagnosis of stroke, recruited from an inpatient rehabilitation centre in the Netherlands. Mokken scale analysis was undertaken on the admission and discharge scores on the SULCS to investigate the following psychometric properties: whether the items form a scale (monotone homogeneity model fit); whether the instrument assesses a single concept (unidimensionality); whether the items in the instrument are hierarchical for all patients (double monotonicity model fit); and whether there are valid comparisons between different patient subgroups (differential item functioning). Data from group 1A was also used to test for internal consistency, floor and ceiling effects, and to formulate the start-and-stop rules of the SULCS tool. Admission data from a further 146 patients (group 1B) were used to check the adequacy of the start-and-stop rules. A final small cohort of 30 patients was used to determine the feasibility of the SULCS in a clinical setting.

Result

Following the Mokken scale analysis the SULCS was reduced to ten tasks that clearly relate to daily upper limb activities. The scalability coefficients for the ten items of the scale (all >0.3) and the scale itself (0.88 admission and 0.93 discharge) indicated the SULCS is a strong scale. The scale was shown to be unidimensional, invariantly hierarchical (HT was 0.71), and valid when comparing subgroups of differing age, sex, cause, and location of stroke (all crit--values < 40). Furthermore, the scale has excellent internal consistency (reliability coefficients >0.95). The floor effect of the scale was indicated by the total number of minimum scores of admission (14%). The ceiling effect was indicated by the total number of maximum scores on discharge (42%). Start and stop rules mean that it usually takes between three and eight minutes to administer the SULCS. Detailed instructions for administering the SULCS are attached as an appendix to the article.

Conclusion

The SULCS is a feasible instrument for clinical assessment of upper limb capacity in acute and sub-acute stroke patients. This unidimensional, internally consistent, and hierarchical scale allows start and stop rules to be applied to reduce the time taken to administer the test.

Commentary

Efforts to evaluate upper limb function by clinicians in the acute and sub-acute clinical context using existing outcome measures may be frustrated by time constraints, resourcing issues and patient related factors such as fatigue. In addition to lengthy assessment times, other difficulties with existing outcome measures may include: assessment of more than one ICF construct creating interpretation issues; ceiling or floor effects; requirement of specific equipment; or inclusion of tasks that bear little relation to everyday activities.

This article introduces an upper limb assessment tool that is efficient to administer, robust and uses everyday items within the assessment. Mokken analysis is similar to Rasch analysis but is thought to be more appropriate when the number of items in a scale is relatively small, as in this case (van Schuur, 2003). This article does not address psychometric properties such as responsiveness, construct validity, inter-rater reliability, or comparisons with existing measurement instruments. A companion article is referred to by the authors that addresses these issues (comparing the SULCS with the Action Research Arm Test and Rivermead Motor Assessment) and is expected to be published within the next few months (personal communication Houwink, 2011). This will further inform clinicians as to the clinical appropriateness of the instrument.

The development of this scale was undertaken after extensive consultation with rehabilitation physicians, occupational therapists and physiotherapists. However it is unclear how much consultation was undertaken with the target group (stroke patients). The authors acknowledge that other research is needed to validate the SULCS in other settings. Applying this assessment in New Zealand would require using euro coins for item ten of the scale (manipulating coins). Alternatively, and more functionally for the New Zealand setting, the euro 50, 2 and 1 cent coins could be substituted by New Zealand 50, 20 and 10 cent coins. Due to size and weight differences in the coins, it remains to be seen if this change would significantly affect the scale properties and hierarchical order of this assessment. Another item of note is the 42% of patients who scored the maximum 10/10 on discharge. This may indicate insufficient progression of complexity at the top end of the scale, resulting in a ceiling effect. Alternatively as the authors offer, the result may reflect complete recovery of upper limb capacity, however this cannot be verified from the information within the appraised article. Further research is suggested by the authors to investigate adding additional tasks to reduce the ceiling effect.

The SULCS appears to have excellent clinical utility and is likely to be welcomed by therapists, providing its other psychometric properties prove equally robust.

Dave Spence, BPhty

ISIS Rehabilitation Ward, Southern District Health Board, Dunedin

REFERENCES

Houwink A (2011): Personal communication.

van Schuur WH (2003): Mokken scale analysis: between the Guttman scale and parametric item response theory. Political Analysis 11: 139-163.

Roorda LD, Houwink A, Smits W, Molenaar IW, Geurts AC (2011): Measuring upper limb capacity in poststroke patients: development, fit of the monotone homogeneity model, unidimensionality, fit of the double monotonicity model, differential item functioning, internal consistency, and feasibility of the stroke upper limb capacity scale, SULCS. Archives of Physical Medicine and Rehabilitation 92:214-227. (Abstract prepared by Dave Spence)
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