Research Designs - Evaluate evidence for treatment’s effectiveness

SPHR 4118W: Senior Seminar


Levels of Evidence

Reilly et al. (2004)*

As we have discussed in class and as your textbook alludes to, certain types of research designs “carry more weight” when one goes to evaluate the evidence available for a given treatment’s effectiveness.  This table outlines a commonly used rubric for evaluating the level of evidence in research articles on treatment.

Evidence Level Evidence Obtained From Definitions and Study Types
I. A systematic review of all relevant randomized controlled trials** A meta-analysis is a summary of all published randomized controlled trials on the topic of interest.   A systematic review of all published primary studies on the topic of interest.
II. At least one properly designed randomized controlled trial A randomized controlled trial is used to compare one or more interventions or to compare an intervention(s) against no treatment. Participants are randomly assigned to the group(s) and the results of previously defined outcomes are evaluated in treated and non-treated groups.
III. 1 Well-designed controlled trials without randomization Occasionally randomization is not possible for ethical or practical reasons and in these circumstances a controlled trial is undertaken – identical in all respects apart from participants being randomized to treatment groups. This category should be used if randomization procedures are not adequately described.
III. 2 Well-designed cohort or case-controlled analytic studies preferably from more than one centre or research group In a cohort study a group of people, the cohort, are followed over time. The cohort may be studied to examine sub-sets within the cohort (for example, those exposed or not exposed to an intervention or item of interest) or to study the natural history of disease/disorder (for example, speech and language development)   Case-controlled studies involve the comparison of an intervention versus comparison group. They differ from the controlled trials without randomization because they are often retrospective and rely on the identification of a group of people with an outcome or disorder of interest being compared retrospectively with a control group who do not have the outcome of disorder. Case-controlled trials are almost always the design used in rare conditions.
III. 3 Multiple time series with or without the intervention. Dramatic results obtained from uncontrolled experiments. Guyatt et al, (1990) relabeled what psychologists and many allied health researchers term ‘multiple baseline’, ‘single-case’ or ‘single-subject’ research the ‘n of 1 trial’. This involved a single participant and an experiment designed to determine the effect of an intervention.
IV. Opinions of respected authorities based on clinical experience, descriptive studies or reports of expert committees. A case report is usually a preliminary report that described an aspect of an individual (it may be an unusual presentation, diagnosis or response to treatment). Sometimes a number of cases are reported together and this is known as a case series.

**Systematic reviews sometimes include primary studies if few or no RCTs are available.

*Full citation: Reilly, S., Douglas, J., & Oates, J. (2004). Evidence based practice in speech pathology.  London: Whurr Publishers.

Research Designs - Evaluate evidence for treatment’s effectiveness

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