The ADKS belongs to a group of psychometric scales that aim to assess knowledge regarding AD, as this can assist with the development of psychoeducational curricula and interventions for dementia care . The original validation of the ADKS included different populations in the USA (college students, older adults with no cognitive impairment, dementia caregivers, and healthcare professionals), and the scale was also applied to or validated by studying college students in South Korea and Nepal, caregivers in the Netherlands, the United Kingdom, and South Korea, and healthcare professionals in Australia, Brazil, China, India, Malaysia, and Spain [8, 10, 18,19,20,21,22,23,24,25,26,27]. It was also administered to laypeople in Brazil, and was included as a knowledge resource on the website of the Alzheimer’s Association in the USA [26, 28].
Despite some criticisms of the ADKS that are linked to dichotomous item assessment, reverse-scored items, and a likely ceiling effect for some items, this is currently one of the few validated scales to be used either at the intervention planning stage or as a signal or outcome measure when evaluating interventions or the overall knowledge of dementia [7, 8, 29]. Because the ADKS was designed to estimate the overall knowledge regarding AD, not an underlying construct or dimension, several common psychometric statistics such as internal reliability or analyses of dimensional structure are not as relevant as they might be to other scales that are used to evaluate the effectiveness of interventions [7, 8].
Our study shows that the range of percent correct values for ADKS items and the near-symmetric distribution of overall scores may support its usefulness for relatives of people with cognitive impairment who are seeking a neurological evaluation, and to guide the psychoeducational efforts of dementia support groups . However, the results of the IRT approach do not support scale unidimensionality or the ranking of subjects across a continuum of AD knowledge. The AISP indicates that the underlying structure of the ADKS does not fit the originally theorized domains. It instead suggests that items are independent, which is relevant for a general knowledge scale that is used to detect knowledge gaps, but not for ranking individuals.
Carpenter et al.  developed the ADKS in 2009 to incorporate new scientific understanding about AD into the ADKT. All measures require periodic updates to keep pace with developments and new information emerging from the rapidly evolving field of cognitive disorders. In their systematic review of AD knowledge outcome measures, Spector et al. recommend the development of a contemporary instrument that incorporates items relating to biopsychosocial and patient-centered models of AD care . Our results do not support the use of the total ADKS score to meaningfully rank people according to their AD knowledge, as the data did not fit with the MH model. However, even though the IRT results indicate that the ADKS is not suitable for evaluating people at the individual level, it does not directly follow that group mean scores based on knowledge accrued from multiple independent items are not suitable for comparing population subgroups in terms of their AD knowledge, as our meta-analytical results show. In fact, what might be argued is that the ADKS is a useful outcome measure for evaluating the effectiveness of interventions. When Hattink et al. evaluated an e-learning course for dementia caregivers, they did not find a significant difference between subjects randomized to the experimental psychoeducational intervention (n = 37, mean ADKS score = 24.37, SD = 2.94) and those randomized to the control intervention (n = 46, mean ADKS score = 24.39, SD = 2.90) . The mean difference (MD) was not significantly different between groups (MD − 0.02, 95% CI − 1.30 to 1.26) and did not show a significant change at four months from baseline (n = 83, mean ADKS score = 24.28, SD = 3.35). However, even given the serious doubts regarding the use of ADKS as an outcome measure to evaluate interventions, knowledge of the correctness of responses may be useful when designing and developing interventions aimed at improving AD knowledge among caregivers and health professionals—aims that also guided the development of the ADKS .
This study has several limitations. There is participant self-selection bias; it is possible that the survey tended to attract the most motivated respondents or those who were most knowledgeable about AD. In addition, carrying out the study in only one company may have limited the generalizability of the findings to other healthcare communities, or even the general population.