We currently lack basic epidemiological information (prevalence, incidence of cognitive deficits) on cognitive impairment within specific chronic disease groups (diabetes, cardiovascular disease, obesity, chronic obstructive pulmonary disease, and renal insufficiency) at different ages, particularly younger adults and middle-aged adults who are currently of working age. Previous work has focussed on the elderly and studies often lacked sufficient numbers in younger age groups to conduct valid analyses. Using our previously published methods of data pooling, meta-analysis and integrative analysis, we will draw on a wide range of available data including international collaborative cohort studies, to address these research questions. Prevalence estimates and modifying factors will be identified from multiple studies and reported in a series of meta-analyses to be published in high impact journals. Diabetes, chronic obstructive pulmonary disease, cardiovascular disease and renal disease will be examined individually and in combination, adjusted for confounders. Propensity scores (estimates of the probability of a being diagnosed with a specific disease conditional on a specific set of confounders) will be used; estimates will be reported of both mean differences in key cognitive indicators, and clinically significant cognitive impairment.