An effectiveness frontiers-based approach may be used to study the relationship between, on the one hand, the cognitive functions of people aged over 50 in Europe and, on the other hand, various other factors, especially age, education and involvement in activities, professional or otherwise. The aim is to construct a «frontier» which corresponds to the optimal cognitive performance which each individual should be able to attain given their age and level of education. To this end, we use individual data collected during the first wave of the international interdisciplinary Share 2004 survey, which contains the results of cognitive tests carried out on more than 22,000 older people and information on their state of mental and physical health, socio-economic status, family entourage, their professional and non-professional activities, social isolation, and their individual cognitive performances, measured using tests. In addition to the fundamental role played by education in the fight against cognitive ageing, remaining in economic activity, along with involvement in a non-professional activity or physical activities ­ vigorous and moderate ­ are positively linked to the build-up of individuals' "cognitive reserves". The availability of data from successive series of Share surveys, which are carried out every other year using the same field, may make it possible to determine the underlying causal relationships.