After you have collected the relevant articles, you will now assess the quality of the research method described in the article.
When critically appraising a study, it is important to think about the following questions:
One other aspect to consider is the sample size. From Bandolier:
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.
A Case Report is a description of one person with an unique or interesting condition. A Case Series is a description of several people with unique or interesting conditions. This is completely descriptive in nature.
Cross-Sectional study designs simply describes a sample population at one point in time. It is descriptive in nature.
Case Control study design simply compares a sample population with certain conditions or characteristics and compares them with a sample population without the certain conditions or characteristics. This design is descriptive and historical/retrospective in nature.
Cohort study design has defined sample population with a specified condition or treatment that is followed over time with another sample population. The population can be followed prospectively into the future or retrospectively into the past. It is descriptive in nature.
Randomized Controlled Trials are experimental studies where an intervention is applied to one group and the other group (control) does not get the intervention or gets placebo. Typically, subjects are randomized into the intervention or control group.
"A Systematic Review is a comprehensive survey of a topic that takes great care to find all relevant studies of the highest level of evidence, published and unpublished, assess each study, synthesize the findings from individual studies in an unbiased, explicit and reproducible way and present a balanced and impartial summary of the findings with due consideration of any flaws in the evidence. On the other hand, Meta-analysis is a systematic, objective way to combine data from many studies, usually from randomized controlled clinical trials, and arrive at a pooled estimate of treatment effectiveness and statistical significance." (Koffel, 2011)