What is a major drawback of longitudinal designs?

What is a major drawback of longitudinal designs?

• A. They can be distorted by biased sampling, selective attrition, and cohort effects.
• B. They have no drawbacks.
• C. They are always quicker than cross-sectional designs.
• D. They eliminate practice effects.

Answer: (A)

Longitudinal studies have the strength of showing how individuals change over time by following the same people, but they also carry notable drawbacks. The big issue is that the sample can become distorted as the study progresses. Biased sampling can occur if the initial participants aren’t perfectly representative of the population, and selective attrition happens when people drop out for reasons related to the study variables (for example, those with lower cognitive performance leaving the study). This means the remaining participants may no longer represent the original population, which can skew findings about developmental change. Cohort effects add another layer: since the study follows a group born around the same time, their shared historical experiences can influence development in ways that aren’t due to aging per se, making it hard to separate true developmental change from era-specific influence. Together, these factors can threaten the validity of conclusions drawn from longitudinal data, which is why this drawback is often highlighted.

Longitudinal studies have the strength of showing how individuals change over time by following the same people, but they also carry notable drawbacks. The big issue is that the sample can become distorted as the study progresses. Biased sampling can occur if the initial participants aren’t perfectly representative of the population, and selective attrition happens when people drop out for reasons related to the study variables (for example, those with lower cognitive performance leaving the study). This means the remaining participants may no longer represent the original population, which can skew findings about developmental change. Cohort effects add another layer: since the study follows a group born around the same time, their shared historical experiences can influence development in ways that aren’t due to aging per se, making it hard to separate true developmental change from era-specific influence. Together, these factors can threaten the validity of conclusions drawn from longitudinal data, which is why this drawback is often highlighted.