2.1.1. Cross-sectional studies

Cross-sectional studies are a point-in-time study, such as a one-time disease surveillance survey, and are typically used to estimate disease prevalence or the simultaneous association between a risk factor and  a disease. In this design, the exposure and outcome for each subject in the study are ascertained simultaneously. This simultaneity often leads to difficulty in conclusively establishing the temporal relationship between the exposure and the outcome. It is also important to note that chronic conditions are more likely to be identified in a survey because they are more likely to persist in a population and are more common. Therefore this study design is less useful for studies of rare exposures and rare outcomes. However, cross-sectional studies can be inexpensive, relatively quick to conduct, and are used to identify potential associations between exposures and outcomes that warrant further research with more rigorous population-based study designs. An example of a cross-sectional study is when a bee inspector examines hives in an apiary for characteristics, such as size, strength, activity, and disease and then uses these data to generate estimates of the prevalence of hives with a particular disease (e.g., Chalkbrood) in a region. Classification and regression tree (CART) analysis