Descriptive studies are generally classified as either crosssectional or longitudinal. Descriptive studies providing a snapshot or description of business elements at a given time are cross-sectional. Cross-sectional and longitudinal studies both use a sample to describe business activities. Whereas crosssectional studies describe business activities at a single time, longitudinal studies describe events over time. Longitudinal studies are therefore appropriate when research questions and hypotheses are concerned with how things vary over time.