Advanced Dental Admission Test (ADAT)

What is a primary bias observed in prospective cohort studies?

1. Recall bias

2. Selection bias

3. Loss to follow-up

4. Observer bias

The correct answer is: Loss to follow-up

In prospective cohort studies, loss to follow-up is a significant concern because it can introduce bias into the results if the participants who drop out differ systematically from those who remain. As the study progresses over time, some individuals may withdraw for various reasons, such as moving away, experiencing health issues, or a lack of interest. When these individuals leave the study, it can alter the initial population and potentially skew the results by creating a non-representative sample of the original cohort. Retention of participants is crucial for maintaining the integrity of the study findings and ensuring that the outcomes accurately reflect the exposure of the entire group. If a substantial number of participants drop out and these participants have different outcomes compared to those who remain, it can lead to incorrect conclusions about the association between exposure and outcome. Therefore, addressing loss to follow-up is essential in the design and analysis phases of prospective cohort studies to minimize its impact on the validity of the findings.