Final answer:
Prospective cohort studies face limitations like selection bias, loss to follow-up, difficulty in establishing causality, high costs, and limited generalizability. Selection bias arises from non-random participant selection, while loss to follow-up can occur when subjects drop out over time. These limitations affect the study's validity and generalizability.
Step-by-step explanation:
The major limitations of a prospective cohort study include several key challenges, such as selection bias, loss to follow-up, the difficulty in establishing causality, being expensive and time-consuming, and having limited generalizability. This form of observational study tracks a group of similar subjects over time, collecting data periodically to observe the progression of disease states or conditions. The accuracy of cohort studies is often higher than case-control studies due to prospective data collection, allowing researchers to establish a sequence of events. However, these studies often demand significant time and financial resources, which can be a barrier to their execution.
Selection bias occurs when the participants chosen for the cohort are not representative of the larger population due to non-random selection methods. This can lead to skewed results and incorrect conclusions. Loss to follow-up is a common issue in long-term studies; as time goes by, participants may drop out due to various life events or loss of interest, potentially affecting the study's validity. Additionally, while cohort studies are useful for establishing sequences and associations, they often struggle with confirming causality due to potential confounding factors. The high cost and resource demands make these studies less feasible for some researchers, and the time taken to obtain results may make them less appealing for urgent research questions. Lastly, due to the initial selection of participants and attrition over time, the findings from a cohort study might not be generalizable to the entire population, especially if the sample becomes less representative as the study progresses.