What type of studies are generally included in systematic reviews?

Systematic reviews aim to synthesize evidence from a range of studies to address a specific research question, typically concerning the efficacy or effectiveness of an intervention. They focus primarily on intervention studies, which are designed to evaluate the outcomes of specific treatments or interventions. This includes randomized controlled trials (RCTs) and other comparative studies that assess the impact of interventions on health outcomes.

Diagnostic tests can also be included in systematic reviews, particularly if the review seeks to evaluate the accuracy and reliability of different diagnostic methods. The combination of intervention studies and diagnostic tests allows for a comprehensive understanding of how various medical treatments perform and how effective diagnostic methods are in clinical settings.

While other types of studies like observational studies, qualitative research, or meta-analytical approaches contribute valuable insights, they do not align closely with the primary focus of systematic reviews, which are often centered on interventions and diagnostics. This emphasis on intervention studies and diagnostic tests makes the answer to the question stand out as the most appropriate choice.