Evidence-Based Nursing: an Evidence-Based Nursing Tutorial from the Information Services Department of the Library of the Health Sciences-Chicago, University of Illinois at Chicago.
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."
Source: Critical Appraisal. Bandolier.
How do I write this all up? First, you'll need to take notes as you work through your project.
Second, you'll need to state:
Make sure you capture the above information as you go!
Here's an example of a write up: (Look at the section labeled Methods: Study Identification) http://www.biomedcentral.com/1472-6947/10/60#sec2