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Levels of Evidence and Study Design: Overview

Information on study design and levels of evidence to help you evaluate the medical, nursing and health care literature

Purpose of this Guide

This guide is designed to assist health care professionals to become effective and efficient users of the medical and nursing literature.

Why is this Important?

Levels of Evidence

The purpose of evidence-based medicine is to find evidence that can be used to make clinical decisions. Evidence based medicine utilizes a hierarchical system that classifies evidence. Clinicians are encouraged to find the highest level of evidence to solve clinical questions. Levels of evidence provides a guide to help prioritize information.  

Study Design

Study design combines trial methodology and statistical analysis with the goal of deriving conclusions that reflect the truth. The most important aspect of a study is the design. A study that was poorly analyzed can be reanalyzed to make new conclusions. There is no recourse in salvaging a study that was poorly designed. A study’s design dictates best methods for analyzing generated data. This makes study design largely responsible for data credibility and scientific integrity of the study.

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