This article explores how aggregate level data may be used to make inferences about individual level behaviour. A common strategy in the past was to assume that the relations evident in aggregated data are also present in individual data. Analysis of datasets where there is both individual and aggregated information demonstrates that this assumption is most often incorrect. This means that the relationships observed between variables at an aggregated level are unlikely to be observed in individual level data. This is a problem because quite often social scientists only have aggregated data for exploring individual level behaviour. A key question explored in this article is how is it possible to validly and reliably use aggregated datasets to make inferences about relationships between variables at the individual level. An example analysis is given using electoral data from the Czech Republic.
As the probability to marry is stratified and differs for people with certain characteristics, it can be expected that some marriages are more likely to end in divorce than others. Among others in the literature the divorce risk factors are often mentioned: too low or too high age, marriage, educational level (low or high education) or educational or age heterogamy. This article describes the effects of age and education of both spouses and their combinations (heterogamy or homogamy) on the stability of marriage in the Czech Republic between 1994 and 2007. Analysis (using event history analysis) is based on data from the Czech Statistical Office and examines those individuals who entered into marriage in 1994. Although, the effect of age at marriage itself is found to be weak, the interaction between age at marriage for men and women exhibits more significant effects. The relationship between education and divorce risk takes the form of an inverted U: people with basic education and people with higher education have the lowest risk of divorce. The assumption of greater stability among homogamous couples is not observed; however, the probability of divorce is higher among heterogamous marriages where the woman is older or has higher education than man.