Reliability and Validity of the Thai Version of the PAINAD Scale: An Extended Application of Pain Assessment in the Moderately Severe Stage of Dementia

Objective: To evaluate the reliability and validity of the Thai version of the PAINAD (PAINAD-Th) scale for assessing pain in people with dementia (PwD). Materials and methods: A cross-cultural translation of the PAINAD scale involving forward and back-translation to and from Thai was conducted, and then the content validity index (CVI) of semantic equivalence was evaluated. The PAINAD-Th was tested on 120 videos of PwD. Each participant was recorded in two videos: one during an activity and the other at rest. Subsequently, two trained nurses independently observed the videos and rated the PAINAD-Th to assess inter-rater reliability. The rating process was repeated in one week to investigate the test-retest reliability. The concurrent validity was assessed against the Visual Analogue Scale rated by the expert committee. Results: The CVI of PAINAD-Th was 1.00 for forward translation and 0.93 for back translation. The PAINAD-Th showed strong correlations with the reference standard (r_s=0.854–0.943, p-value < 0.001). The inter-rater agreement for the total scores was 0.937 and 0.955, and the test-retest reliabilities were 0.914 to 0.964 for the activity stage and 0.880 for the resting stage, respectively. The concurrent validity index did not vary significantly across different stages of dementia; the findings remained consistent in the delirium subgroup analysis. Conclusions: The PAINAD-Th is a valuable tool for evaluating pain in PwD, not only in severe dementia but also in moderately severe stage, regardless of concurrent delirium. It also demonstrated good-to-excellent concurrent validity, inter-rater reliability, and test-retest reliability.