Cross-sectional studies are used to provide a snapshot of disease and other variables in a defined population at one point in time. Data can be used to infer relationships between a disease and other variables, however, as the data is gathered simultaneously, chronological sequences of exposures and outcomes cannot be determined. Some cross-sectional studies are purely descriptive, in that they just describe the number of cases or number of events in a particular population at a point in time or over a period of time.