Final answer:
Cross-sectional studies measure exposure and outcome at the same point in time. They are observational and do not establish causal or temporal relationships like longitudinal studies do.
Step-by-step explanation:
Cross-Sectional Studies
Cross-sectional studies are a type of observational study that collect data from a sample of subjects at a single point in time. These studies can identify potential associations between exposure and outcomes such as disease occurrence but do not establish causal relationships. These studies are quick and cost-effective but are limited by their inability to determine temporal relationships or changes over time, unlike longitudinal studies that follow subjects over a period of time to see changes and trends.
Based on the definitions, the correct answer to the question is:
Exposure and outcome at the same point in time
This defines what cross-sectional studies measure, which is to observe potential associations between different variables at a particular moment without confirming causation or the direction of the relationship.