Psychometric Testing of the Valued Life Activities Questionnaire in People with Rheumatoid Arthritis in the UK: Rasch Analysis.
Prior, Y & Tennant, A & Hammond, A 2015, 'Psychometric Testing of the Valued Life Activities Questionnaire in People with Rheumatoid Arthritis in the UK: Rasch Analysis.', Arthritis and Rheumatol., 67:10.
Background/Purpose: Developed in the USA, the Valued Life Activities Scale
(VLAs) measures participation in daily activities. We have linguistically and
culturally adopted the VLAs 33 item scale for use in the adults with RA in the
United Kingdom (UK) using the recommended guidelines for cultural adaptation.
Methods: We recruited participants through 17 Rheumatology clinics in National
Health Service (NHS) Hospitals across the UK. The internal construct validity
(unidimensionality) was assessed using (i) Confirmatory Factor Analysis (CFA)
(ii) Mokken scaling and (iii) Rasch model (including the stochastic ordering of
items, unidimensionality and local independence). The RUMM2030 software was
used, utilising the partial credit parameterisation of the Rasch model.
Results: Responders (n=340) had a mean age of 62 years (SD 12.1), and average
disease duration was 14.4 years (SD 11.7). Of these, 73.8% were women and a
third (32.3%) were employed. Just over half (55.9%) were on combination
therapy, and 7.4% were on biologic drugs. A CFA failed to support a total score
from the 33 items (Chi Square 3552:df 464:p<0.0001; RMSEA 0.066 (90% CI:
0.064-0.068); CFI .985; TLI 0.984); the 25 items (Chi Square 2836:df
275:p<0.0001; RMSEA 0.078(90CI: 0.076-0.081); CFI .987; TLI 0.986; or the 14
item version (Chi Square 1228:df 77:p<0.0001; RMSEA 0.099(90CI:
0.094-0.104). Based on the 25 item version the three domain structure (i.e. Obligatory,
Committed and Discretionary activities) of the item set also failed (Chi Square
2693:df 272:p<0.0001; RMSEA 0.076(90CI: 0.074-0.079); CFI .987; TLI 0.986). Fit of the data from the VLA to the
Rasch model is shown in Table 1. The stochastic ordering (fit) and
unidimensionality assumptions were not satisfied. The VLAs was characterised by
multidimensionality and misfit, which may have been influenced by extensive
clusters of residual item correlations. While reliability was high in all
cases, this could be expected to be inflated in the presence of local response
dependency, as identified through the residual correlation patterns.
Unfortunately, out of the 1545 cases collected in
this study, only 79 subjects had complete data on the items that comprise the
‘activities’ (obligatory + committed) and ‘participation’ (discretionary)
domains, due to the ‘does not apply to me’ response option.
Conclusion: The UK version of the VLA, across various scales, fails to
satisfy classical and modern psychometric standards. The raw score cannot be
considered a valid estimate of the persons’ ability within any domain. The
‘does not apply to me’ response option renders valid scoring impossible in
routine settings. It is recommended that the VLA set of items should be
reconfigured and considered as a measure of Activities and Participation,
consistent with ICF terminology.
Arthritis and Rheumatol., 67:10.