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

Background Better 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. Methods We 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≤24 or MoCA≤25, SAGEA≥7), and with a country-standardised z-score threshold of cognitive or functional score of ≤-1. Results In 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≤24 or MoCA≤25 ranged from 23–36%; the proportion below a country-standardised z-score threshold of ≤1 ranged from 10–14%. The differences in prevalence of impaired IADL (SAGEA≥7) ranged from 2–6% and by country-standardised thresholds from 3–6%. Conclusions Accounting 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 statement We 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 Points 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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors