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Longitudinal Study Design

A longitudinal study is a correlational research study that involves repeated observations of the same items over long periods of time. Longitudinal studies are often used in psychology, for example, to study developmental trends across the life span. The reason for this is that unlike cross-sectional studies, longitudinal studies track the same people, and therefore the differences observed in those people are less likely to be the result of cultural differences across generations. Longitudinal studies are also used in medicine to uncover predictors of certain diseases. Because longitudinal studies are observational, in the sense that they observe the state of the world without manipulating it, it has been argued that they may have less power to detect causal relationships than do experiments. But because of the repeated observation at the individual level, they have more power than cross-sectional observational studies, by virtue of being able to exclude time-invariant unobserved individual differences, and by virtue of observing the temporal order of events.

Longitudinal studies allow social scientists to distinguish short from long-term phenomena, such as poverty. If the poverty rate is 10% at a point in time, this may mean that 10% of the population is always poor, or that the whole population experiences poverty for 10% of the time. It is not possible to conclude which of these possibilities is true by using a cross-sectional study. Types of longitudinal studies include cohort studies and retrospective studies. Cohort studies sample a cohort, defined as a group experiencing some event in a selected time period, and studying them at intervals through time. A retrospective study is a longitudinal study that looks back in time. For instance a researcher may look up the medical records of previous years to look for a trend.

Walker Downey & Associates, Inc. can use longitudinal study design/analysis to maximize the power of the client’s research investigations.

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