But because many of these were case

But because many of these were case-control studies, where people who already have a certain health outcome (cases) are compared to people who do not have that outcome (controls), it is possible that the results may have been skewed by problems inherent in these types of studies; people with illnesses, for example, often recall past behaviors differently from those without illness, which can lead to potential inaccuracy in the information that they provide to study investigators.