Katz index of activities of daily living in assessing functional status of older people: Reliability and validity of Sinhala version

Purpose

This study evaluated the reliability and validity of the Sinhala version of Katz index of activities of daily living (ADL) in assessing the functional status of older people aged >65 years.

Materials and methods

The Katz index was translated to Sinhala, cross-culturally adapted and administered in two stages. In stage 01, 200 patients aged ≥65 years, selected randomly from out-patient medical clinics, were asked to fill the Sinhala version of Katz index along with the Sinhala version of the 10-item Barthel index (BI). The Katz index was re-administered after two weeks among a subgroup of 45 patients selected randomly. In stage 02, Katz index was administered among randomly selected 200 community dwelling older people, aged ≥65 years. In addition, performance-based physical functions [gait speed (GS) and short physical performance battery (SPPB)] were also measured.

Results

The analysis of stage 01 data showed internal consistency measured with Cronbach's alpha of 0.82 and test-retest reliability evaluated with intra-class correlation (ICC) (95% CI) of 0.94 (0.89–0.96) (p < 0.001). Exploratory Factor Analysis with the Principal Component Analysis revealed the presence of two factors with Eigen value exceeding 01, explaining 75.9% of cumulative variance. Further, the Sinhala version of Katz index total score showed a strong correlation with the BI total score (r = 0.91, p < 0.001) indicating strong concurrent validity. The stage 02 data revealed that older people with poor perception of general health status had lower mean (SD) Katz index score (3.58 ± 1.82) compared to those with good perception of health (5.56 ± 0.79) (p < 0.001). Similarly older people with prevalent diseases had comparatively lower scores of Katz index, compared to those without, indicating the known group validity (p < 0.05). Further, moderate correlations between the Katz index and performance based physical functions were observed showing the agreement (with GS – r; −0.26, p < 0.001, with SPPB – r; 0.31, p < 0.001).

Conclusions

We conclude that the Sinhala version of Katz index has satisfactory psychometric properties and it is a reliable and valid tool to assess the functional status of Sinhala conversant older people in Sri Lanka.