Development, initial validation and reliability testing of a web-based, generic feline health-related quality-of-life instrument

Abstract

Objectives: The objective of this study was to develop a valid, reliable, web-based generic feline health-related quality-of-life (HRQoL) questionnaire instrument to measure the affective impact of chronic disease.

Methods: A large initial item pool, obtained through interviews with cat owners, was reduced using predetermined criteria, survey scores for relevance and clarity, and the ability of individual items to discriminate between healthy and sick cats when owners completed a prototype questionnaire. Using these data, factor analysis was used to derive a scoring algorithm and provide evidence for factorial validity. Validity was demonstrated further in a field trial using a 'known groups' approach (sick vs healthy cats will have a different HRQoL profile, and the HRQoL profile of cats will deteriorate as comorbidities increase). Test-retest reliability was assessed using intra-class correlation coefficients (ICCs).

Results: In total, 165 items were reduced to 20 and, on the basis of a factor analysis that explained 72.3% of the variation in scores input by 71 owners of 30 healthy and 41 sick cats using the prototype, these were allocated to three domains (vitality, comfort and emotional wellbeing [EWB]) with a scoring algorithm derived using item loadings. Subsequently, the owners of 36 healthy and 58 sick cats completed one or two (n = 48) assessments. Median scores (healthy vs sick) for all domains were significantly different ( P <0.001), 78% of cats were correctly classified as healthy or sick and for comorbidities the correlation coefficients were moderate (vitality 0.64; comfort 0.63; EWB 0.50). Test-retest reliability was good (ICC vitality 0.635; comfort 0.716; EWB 0.853).

Conclusions and relevance: This study provides initial evidence for the validity and reliability of a novel HRQoL instrument to aid the assessment and management of chronic diseases of cats.

Figure 1

Summary of the study design for developing a generic health-related quality-of-life (HRQoL) instrument for cats

Figure 2

Examples of dot plots for items that were (a) excluded and (b) retained on the basis of their discriminatory potential as assessed by the research team. The x-axis represents the response values selected by owners of healthy (red square) and unhealthy (blue circle) cats

Figure 3

Plots of scores for three domains of health-related quality of life (HRQoL; vitality, comfort and emotional wellbeing [EWB]) generated by the owners of 36 healthy control cats and 58 sick cats using the 20-item web-based generic HRQoL instrument. Each blue box represents the scores obtained for between 25% (bottom line) and 75% (top line) of the group, with the line in the middle representing the median score

Figure 4

Fitted line plots of linear regressions performed for three domains of the health-related quality-of-life (HRQoL) instrument. Statistics presented include the residual standard deviation (S) and r values for the three domains. The number of presenting conditions is on the x-axis, whereas the HRQoL scores are on the y-axis