Chapter 2 What is Evidence?

Objectives Discuss the concept of “best available clinical evidence.” Describe the general content and procedural characteristics of desirable evidence and their implications for the selection of studies to evaluate. Describe different forms of evidence and their uses for answering clinical questions in physical therapist practice. Discuss and apply the principles and purposes of evidence hierarchies for each type of clinical question. Discuss the limitations of evidence hierarchies and their implications for the use of evidence in practice.

What Qualifies as Evidence? Guyatt and Rennie - “any empirical observation about the apparent relation between events constitutes potential evidence.” For example: –Published research articles –Clinical practice guidelines –Patient/client records –Clinician recall of prior patient/client cases Sackett et al – “best available clinical evidence”

Preliminary Quality Criteria Relevance –Question posed –Patient involved Research process –Peer review –Contemporary timing

Research Design Overview Design options that address bias –Randomization techniques to distribute subjects into groups; –The use of more than one group in order to make a comparison; –Controlled experimental manipulation of the subjects; –Measures at the patient/client level (e.g., impairment in body functions and structure, activity limitations, participation restrictions); and/or –A systematic method for collecting and analyzing information.

Research Designs - Timing Prospective – a research design that follows subjects forward over a specified period of time. Retrospective – a research design that uses historical (past) data from sources such as medical records, insurance claims, or outcomes databases. Cross-sectional – a research design that collects data about a phenomenon during a single point in time or once within a defined time interval. Longitudinal – a research design that looks at a phenomenon occurring over time

Research Design – What is the Question? The question posed for study guides choices about the research design For example: –Usefulness of diagnostic test/clinical measure – researchers may choose a cross-sectional non-experimental design –Effectiveness of intervention – researchers may choose a cross- sectional or longitudinal experimental design

Evidence Hierarchies Ranking schemes in which research designs are ordered from highest to lowest in terms of bias control Intended to facilitate the efficiency of the evidence selection process Details vary because research designs are dictated by the question posed Systematic reviews of high quality studies are at the top of all traditional hierarchies

Evidence Hierarchy Limitations Variability in quality rating systems used to classify evidence Inconsistent reliability and validity testing Serve as a “screening tool” only – study or pre-appraised product must be evaluated on its own merits