Panel Study is a form of longitudinal research in which a panel of respondents or subjects is selected and then followed or interviewed over time. In a Panel Study, Panel members are often difficult to recruit because of an unwillingness to fill out questionnaires or submit to interviews several times. In a Panel Study, if a panel of first year university students is selected the researcher would, for example, be able to learn what their routes are towards an undergraduate degree. Drawing a sample of undergraduates at year one, year two and year three would not provide the same degree of detail.
Once the sample has been secured, the problem of mortality emerges. Some panel study members will drop out for one reason or another. Because the strength of panel studies lies in interviewing the sample size at different times, this advantage diminishes as the sample size decreases. Panel studies are often vulnerable to instrumentation threat if the researcher in panel studies is not confined to the variables measured in the original study. In the intervening time, new variables might have been identified as important, but if those variables were not measured during the original survey, they are unavailable to the researcher.
Panel study data are particularly useful in predicting long-term or cumulative effects which are normally hard to analyze in a one-shot case study (or cross-sectional research study). Panel studies measure the same sample of respondents at different points in time. Unlike trend studies, panel studies can reveal both net change and gross change in the dependent variable. Additionally, panel studies can reveal shifting attitudes and patterns of behavior that might go unnoticed with other research approaches. Depending on the purpose of the study, researchers can use either a continuous panel study, consisting of members who report specific attitudes or behavior patterns on a regular basis, or an interval panel study, whose members agree to complete a certain number of measurement instruments only when the information is needed. In general, panel studies provide data suitable for sophisticated statistical analysis and might enable researcher to predict cause-effect relationships.