Developing a shortened version of the dementia knowledge assessment scale (DKAS-TC) with a sample in Taiwan: an item response theory approach

BACKGROUND: The 25-item Dementia Knowledge Assessment Scale (DKAS2) is a widely used tool for measuring knowledge of dementia. To increase the applicability of the Chinese-language version of the tool (DKAS-TC) for the general public, this study aimed to develop a shortened version using the item response theory (IRT) approach. METHODS: A total of 401 participants voluntarily completed a Chinese-language version of the DKAS2 questionnaire (DKAS-TC) at the start of dementia awareness training courses in 2020 and 2021. The four Rasch family models were used to analyze the dimensionality of the shortened scale (the DKAS-s) and to confirm its accuracy in measuring dementia knowledge. RESULTS: The results justified supported the use of a dichotomous response scale for responding to the DKAS-s and demonstrated good fit of the data to a Rasch model with the four dimensions of “Causes and Characteristics”, “Communication and Engagement”, “Care Needs”, and “Risks and Health Promotion”. Moreover, we shortened the DKAS-TC by selecting items that had both above-average discriminative ability and above-average information. The DKAS-s retained 64.13% of the information contained in the DKAS-TC, resulting in a 16-item scale which retained four items in each of the original four dimensions. The DKAS-s also correlated highly (≥0.95) with the DKAS-TC and exhibited a sizeable range of difficulty of dementia knowledge. CONCLUSIONS: The DKAS-s is expected to be more efficient in field settings while retaining an acceptable level of psychometric properties when used as a survey instrument to measure the general public’s knowledge of dementia. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-022-03596-1.