Level of Evidence Lecture 4

Definition: The National Cancer Institute defines levels of evidence as "A ranking system used to describe the strength of the results measured in a clinical trial or research study. The design of the study (such as a case report for an individual patient or a randomized double-blinded controlled clinical trial) and the endpoints measured (such as survival or quality of life) affect the strength of the evidence.

Evidence Pyramid Systematic reviews and meta-analysis are situated at the top of what is known as the “Evidence Pyramid” (see figure below). As you move up the pyramid the amount of available literature on a given topic decreases, but the relevancy and quality of that literature increases. Systematic reviews and meta-analysis are considered to be the highest quality evidence on a research topic because their study design reduces bias and produces more reliable findings. However, you may not always be able to find (or need to find) the highest level of evidence to answer your research question. In the absence of the best evidence, you then need to consider moving down the pyramid

Meta-analysis Combines the results of different studies Estimate an average or common effect. The highest level for evidence based medicine!

Systematic Reviews Identify all relevant published and unpublished evidence Select studies or reports for inclusion evaluate the quality of each study or report Synthesize the findings from individual studies or reports in an unbiased way Interpret the findings and present a balanced and impartial summary of the findings with due consideration of any fault in the evidence. Bias= baiased = prejudge Impartial= natural assess= judge

Randomized control trails RCT is a type of scientific(medical) experiment, where the people being studied are randomly allocated one or other of the different treatments under study. The RCT is often considered the gold standard for a clinical trial. RCTs are often used to test the efficacy or effectiveness of various types of medical intervention and may provide information about adverse effects, such as drug reactions. Intervention = mee bemoeien

Cohort studies a type of medical research used to investigate the causes of disease, founding links between risk factors and health outcomes. Cohort studies are usually forward- looking Retrospective cohort study; means to take a look back at events that already have taken place

Cohort studies Cohort =unit

Case-control studies a case-control study is always retrospective because it starts with an outcome then traces back to investigate exposures. Is designed to help determine if an exposure is associated with an outcome.

Using Pubmed

Questions?