Global variation in tests of cognitive and physical function: analysis of six international randomized controlled trials

BackgroundBetter understanding of global variation in simple tests of cognition and function would aid the delivery and interpretation of multi-national studies of the prevention of dementia and functional decline. MethodsWe aim to describe the variation in simple measures of cognition and function by world region, study, recruitment centre or individual level factors. In six RCTs that measured cognition with the mini-mental state examination (MMSE), Montreal cognitive assessment (MoCA), and instrumental activities of daily living (IADL) with the Standardised Assessment of Everyday Global Activities (SAGEA), we estimated average scores by global region with multilevel mixed-effects models. We estimated the proportion of participants with cognitive or functional impairment with previously defined thresholds (MMSE[&le;]24 or MoCA[&le;]25, SAGEA[&ge;]7), and with a country-standardised z-score threshold of cognitive or functional score of [&le;]-1. ResultsIn 91,396 participants (mean age 66.6{+/-}7.8 years, 31% females) from seven world regions, all global regions differed significantly in estimated cognitive function (z-score differences 0.11-0.45, p<0.001) after accounting for individual-level factors, centre and study. In different regions, the proportion of trial participants with MMSE[&le;]24 or MoCA[&le;]25 ranged from 23-36%; the proportion below a country-standardised z-score threshold of [&le;]1 ranged from 10-14%. The differences in prevalence of impaired IADL (SAGEA[&ge;]7) ranged from 2-6% and by country-standardised thresholds from 3-6%. ConclusionsAccounting for country-level factors reduced large differences between world regions in estimates of cognitive impairment. Measures of IADL were less variable across world regions, and could be used to better estimate dementia incidence in large studies. Impact statementWe certify that this work is novel. After analysing data from a large cohort of participants with a history of cardiovascular disease or cardiovascular risk factors, who were recruited in six international randomised controlled trials (RCTs) we found that accounting for country-level factors reduced large differences between world regions in estimates of cognitive impairment, while measures of functional impairment were less variable across world regions. Key PointsO_LICognitive and functional test scores in randomized controlled clinical trial cohorts vary widely across world regions. C_LIO_LIThe difference in cognitive test performance was large in comparison to difference in measures of activities of daily living (ADLs). Accounting for country-level factors reduced the differences between world regions in estimates of cognitive impairment. C_LIO_LICognitive test measures were less variable and could be used to better estimate dementia incidence in international studies. C_LI Why this study matters?We found that cognitive and functional test scores in RCT cohorts varied widely across world regions. The difference in cognitive test performance was large in comparison to difference in measures of activities of daily living. The impact of differences on the performance of cognitive tests, which were developed in high-income countries, creates challenges for harmonized studies of cognitive decline prevention in different world regions. Future studies using the same test around the world could standardise cognitive score by country, and consider using in addition measures of instrumental and basic activities of daily living, where there is less variation across world regions.