Secular trends in the incidence of dementia in high-income countries: a protocol of a systematic review and a planned meta-analysis.

INTRODUCTION: A global dementia epidemic is projected for the year 2050 with an ever-rising number of individuals living with the syndrome worldwide. However, increasingly, studies are emerging from high-income countries (HIC) that show a positive trend towards a possible decrease in dementia occurrence. Therefore, we aim to systematically summarise evidence regarding secular trends in the incidence of dementia in HIC. METHODS AND ANALYSIS: We will conduct a systematic review of the literature on secular trends in dementia incidence in HIC according to the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) and the Meta-analysis of Observational Studies in Epidemiology (MOOSE) statements. To do so, we will search the databases MEDLINE (PubMed interface), EMBASE (Ovid interface) and Web of Science (Web of Science interface), as well as the grey literature on unpublished studies. To be eligible, studies must have been published in English or German since 1990 and provide sufficient information on prespecified eligibility criteria regarding outcome measurement and methodological approach. Study selection, data extraction and risk of bias assessment will be performed independently by 2 reviewers. Disagreement will be resolved by discussion and/or the involvement of a third researcher. Data abstraction will include study and participant characteristics, outcomes and methodological aspects. Results will be described and discussed regarding methodology. Depending on the number of studies found and the heterogeneity between the studies, we plan to combine outcome data through meta-analysis in order to get pooled incidence measures. ETHICS AND DISSEMINATION: No primary data will be collected; thus, ethical approval is not required. The results will be disseminated through a peer-reviewed publication and conference presentations. PROSPERO REGISTRATION NUMBER: CRD42016043232.