Were the groups similar at the start of the trial?
This is usually reported in the 'Table 1' of the article. If the groups aren't similar, we need to see if there was an adjustment made for the potentially important prognostic factors.
The medical and surgical groups were similar in NASCET. For example, the percentages of patients who were prescribed antihypertensive or antilipidemic medications were similar.
If the study fails any of the above criteria, we need to decide if the flaw is significant and threatens the validity of the study. If this is the case, we'll need to look for another study. Returning to our clinical scenario, the paper we found satisfies all the above criteria and we will proceed to assessing it for importance.
- Was the assignment of patients to treatment randomized? And, was the randomization list concealed?
- Was follow-up of patients sufficiently long and complete?
Were all patients analyzed in the groups to which they were randomized?
And some less important points:
- Were patients and clinicians kept blind to treatment?
- Were groups treated equally, apart from the experimental therapy?
- Were the groups similar at the start of the trial?