What is the main difference between cross-sectional and longitudinal studies?

The distinction between cross-sectional and longitudinal studies lies primarily in the timing and frequency of data collection. Cross-sectional studies are designed to collect data at a single point in time, allowing researchers to examine a snapshot of a population or phenomenon. This approach is useful for identifying trends or relationships without the need for extended observation or repeated measurements.

In contrast, longitudinal studies involve collecting data over an extended period, which allows researchers to observe changes and developments over time. This repeated measurement can provide deeper insights into causal relationships and trends, making longitudinal studies more complex and typically more resource-intensive.

Due to the nature of data collection, cross-sectional studies are often less expensive and faster to conduct than longitudinal studies. However, the key characteristic that defines a cross-sectional study is its single time point of data collection, making option C the correct choice.