Figure 1

Flowchart of study selection for systematic review and meta-analysis. Notes: MEDLINE searches (1990–2012) included the following: (1) “Risk factor” as MESH term AND “Dementia” in title; (2) “Risk factor” as MESH term AND “Alzheimer” in title; (3) “Risk factor” as MESH term AND “Alzheimer” in title; (4) “Risk factor” as MESH term AND “cognitive” in title; (5) “Risk factor” in title and “cognitive” in title. Given that each search is not mutually exclusive of other searches, there were duplicates which were deleted from the final number of included studies. The following notations are defined follows: N1 = Studies excluded from all searches combined due to small sample size; N2 = Studies excluded from all searches combined due to design being neither cross-sectional nor cohort; N3 = Studies excluded from all searches combined due to being a review or a letter to the editor; N4 = Studies excluded from all searches combined due to lack of relevance to topic or hypothesis; N5 = Studies excluded from all searches combined for other reasons (e.g. special group of people); N6 = Final included studies; N6a = Final included cohort studies; N6b = Final included cross-sectional studies.