Criteria for Appraisal
When appraising research, keep the following three criteria in mind:
Quality: Trials that are randomized and double blind, to avoid selection and observer bias, and where we know what happened to most of the subjects in the trial.
Validity: Trials that mimic clinical practice, or could be used in clinical practice, and with outcomes that make sense. For instance, in chronic disorders we want long-term, not short-term trials. We are [also] ... interested in outcomes that are large, useful, and statistically very significant (p < 0.01, a 1 in 100 chance of being wrong).
Size: Trials (or collections of trials) that have large numbers of patients, to avoid being wrong because of the random play of chance. For instance, to be sure that a number needed to treat (NNT) of 2.5 is really between 2 and 3, we need results from about 500 patients. If that NNT is above 5, we need data from thousands of patients.
These are the criteria on which we should judge evidence. For it to be strong evidence, it has to fulfill the requirements of all three criteria.
A literature review matrix allows you to organize your sources and compare a range of studies across a variety of elements. Each matrix should include author, date, and purpose; you can determine the other categories based on the factors that you'd like to focus on (i.e. methodology, population sample, variables, etc.).
Start by organizing your sources in chronological order. This will be useful for observing change in the research over time.
As you read all of the studies, consider which elements of the research process are significant and worth comparing for your literature review. See below for a literature review matrix sample and an Excel spreadsheet template.
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