Why might researchers experience bias in longitudinal studies?

Researchers might experience bias in longitudinal studies because they follow the same participants over many years. This prolonged engagement with the same individuals can lead to a number of influences that might skew results. For instance, as researchers become more familiar with their participants, their expectations and interactions may unconsciously influence how they collect and interpret data. Additionally, participants themselves may change over time, altering their responses based on their evolving perspectives or life experiences, which can also introduce bias.

In this context, retaining the same participants across a long duration can affect the consistency and reliability of the data collected, as it may not accurately reflect broader trends that would emerge from a more dynamic or diverse cohort. Such biases can significantly impact the validity of findings in longitudinal studies, which aim to observe changes over time.