Definition:
A cross-sectional study is a type of research study. In cross-sectional studies, a disease (e.g., asthma) and factors thought to cause or prevent the disease (e.g., fruits, vegetables, pollution) are measured simultaneously in a group of individuals.
Cross-sectional studies provide a "snapshot" of the relationship between a disease and possible causes or preventive factors in a population at a single point in time. Because these factors are measured at the same point in time, cause and effect relationships cannot be reliably determined -- it is not possible to say whether the disease or exposure to these factors came first.
Randomized controlled trials are much better at determining cause-and-effect relationships.
