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Definition ||Advantages ||Disadvantages Panel data are particularly useful in answering questions about the dynamics of change. For example, under what conditions do voters change political party affiliation? What are the respective roles of mass media and friends in changing political attitudes? Additionally, as mentioned above, panel study is useful in predicting long-term or cumulative effects which are normally hard to analyze in a one-shot case study (or cross-sectional study). Finally, panel studies help solve the problems normally encountered when defining a theory on the basis of a one-shot study. Since the research progresses over a period time, the research can allow for the influences of competing stimuli on the subject, which might increase external validity of the study. However, this also causes problems in terms of achieving internal validity because the study design does not strictly control for confounding variables. On the negative side, panel members are often difficult to recruit because of an unwillingness to fill out questionnaires or submit to interviews several times. Once the sample has been secured, the problem of mortality emerges. Some panel 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. Another problem related to this mortality issue is that it can hurt internal validity of the study design. As mentioned above, the panel design provides an opportunity for the researcher to make statements about the cause-effect relationships among different variables. There are three necessary conditions for determining cause and effect. The first is time order. Causation is present if and only if the cause precedes the effect. Second, causation can occur only if there is a covariation between the two variables. Third, before effects are attributed to causes, all other alternative explanations must be ruled out. (for more information about establishing cause & effect relationship, try this link). Since the variables are measured over time in panel studies, it is relatively more valid to make causal inferences with temporal order which might be difficult to get in cross-sectional studies. However, it only satisfies the two necessary conditions (time order and covariation). There might be other alternative variable or factor that is causing outcomes. For example, if the mortality rate in a panel study is high, the remaining penalists might differ in regard to the variable under they study. If it is the case, the variation in the panel study may simply reflect this change. Another serious problem is that the study design is vulnerable to testing threat because respondents often become primed to measurement instruments after repeated interviewing, thus making the sample atypical. Finally, 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. In some cases, the researcher might want to modify measurement with different operationalization. In this case, the change in instrumentation, not the variable of the interest, might lead to the outcome. |
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