A cross-sectional study is a type of observational study in which an outcome (for example, the prevalence of heart disease) and exposure (for example, sugar consumption) are measured at a single point in time in a population of interest. The participants in a cross-sectional study can be divided into those with or without the outcome of interest to determine the overall prevalence of a disease (e.g., How many adults over the age of 65 in the United States have heart disease?).

In addition, the prevalence of an outcome can be compared among participants who were and were not exposed to a particular substance or event to determine the association between an exposure and a disease (e.g., What is the prevalence of heart disease among adults who consume more than and less than 35 grams of sugar per day?).

Although cross-sectional studies are valuable for determining associations between outcomes and exposures, they can’t determine causation — we don’t know whether the exposure preceded the outcomes or vice-versa.