Final answer:
Cohort studies are expensive, time-consuming, and often face high attrition rates, but they collect more accurate prospective data compared to case-control studies. They require substantial financial investment as well as time, and they also must deal with the challenge of maintaining a representative sample over time.
Step-by-step explanation:
Disadvantages of a cohort study include being expensive and time-consuming. These types of studies require significant financial investment and can take years or even decades to complete. Additionally, there is often a high rate of attrition as participants may drop out due to various life changes or simply choose to discontinue their participation. As cohort studies are prospective, participants are not required to recall past information, so the issue of participants being untruthful due to recall is less applicable compared to case-control studies, which rely on retrospective data.
Moreover, there are challenges in maintaining a sample that continues to represent the larger population over time. Adjustments may be required as the study progresses to ensure the sample's representation. Observer bias is also a potential disadvantage, but establishing clear criteria for behaviors and having multiple observers can mitigate this issue.