Once you have searched for information, you will need to critically appraise the studies you have found. This is a really important process because it ensures that studies with scientific flaws are disregarded, and the ones you include are relevant to your research question.

When evaluating primary research (research which hasn't been pre-appraised or filtered by others), you need to make sure the evidence you are including in your review is scientifically rigorous. The main questions to address are:

• Is the study relevant to your question?
• How scientifically did the researchers design the study, especially in their care to eliminate bias?
• What do the results mean and are they statistically valid (not just due to chance)?

For a more detailed look at Critical Appraisal, head to the Systematic Review Guide - Critical Appraisal and the Evidence-Based Practic Guide - Appraise.

Critical appraisal of health articles can be very time consuming. Sometimes you just need to quickly decide on the trustworthiness and value of a paper. Here are some things to consider:

• Relevance - Compare the study to your search framework (such as PICO) - is it similar or transferable?
• Results - Were statistical tests applied and did they indicate the findings were statistically significant?
• Applicability to your research question - Did the researchers contribute to an answer to your original question? Is your study group similar to this or quite different? 
• Quality of study – There are many tools out there for a rapid critical appraisal of the study quality. For example, one you could use if you were reviewing controlled clinical trials is the RAMMbo appraisal method (Salisbury, Glasziou, & Del Mar, 2007):

R - Recruitment – were the subjects chosen in the study representative of the target population? Were there enough subjects to make the study valid?

A - Allocation – was the trial randomised?   

M - Maintenance – Was the status of the control group and study group maintained throughout the trial?  Were they treated the same way apart from the intervention?  

M - Measurement (Blinding, Objective measures) – were the outcomes measured objectively and the subjects blinded to the intervention?  Was bias eliminated as much as possible?      

Another great tool for quick appraisal of health articles is from the Medical Research Council in the UK. Understanding Health Research takes you through a series of questions about a particular article, highlighting the good points and possible problem areas. You can print off a summary at the end of your checklist.

See the next box below for some more detailed appraisal tools in the health sciences.

Salisbury, J., Glasziou, P., & Del Mar, C. (2007). Evidence-based practice workbook: Bridging the gap between health care research and practice (2nd ed.). Oxford: Blackwell/BMJ Books.

Fortunately, there have been some great checklist tools developed for different types of studies. Here are some examples:

• The Joanna Briggs Institute (JBI) provides access to critical appraisal tools, a collection of checklists that you can use to help you appraise or evaluate research.
• Critical Appraisal Skills Programme (CASP) is part of Better Value Healthcare based in Oxford, UK. It includes a series of checklists, suitable for different types of studies and designed to be used when reading research.
• The Equator Network is devoted to Enhancing the QUAlity and Transparency Of health Research. Among other functions, they include a Toolkit for Peer Reviewing Health Research which is very useful as a guide for critically appraising studies.
• Critical Appraisal Tools (CEBM) - This site from the Centre of Evidence Based Medicine includes tools and worksheets for the critical appraisal of different types of medical evidence.
• Understanding Health Research - is from the Medical Research Council in the UK. It's a very handy all-purpose tool which takes you through a series of questions about a particular article, highlighting the good points and possible problem areas. You can print off a summary at the end of your checklist

• Critical appraisal tools from the NHS in Scotland links interactively to all sorts of resources on how to identify the study type and build your critical appraisal skills, as well as to tools themselves.