What is an example of a lower level of evidence according to research standards?

Case control studies are considered a lower level of evidence in the hierarchy of research methodologies. This is because they are observational studies that look retrospectively at individuals who have a certain condition (cases) compared to those who do not (controls). While they can provide insights into potential associations and generate hypotheses, they are more prone to bias than higher-level studies such as randomized controlled trials or systematic reviews.

Higher levels of evidence, like randomized controlled trials, involve active intervention and random assignment, which helps establish causation rather than mere associations. Similarly, systematic reviews and meta-analyses synthesize findings from multiple studies, providing a more robust evidence base. In contrast, case control studies can only show correlations and are limited by factors such as recall bias and the inability to control for confounding variables effectively.