Critical appraisal of a scientific article involves using a number of terms and concepts that are taken from epidemiology and statistics. If we use these terms or concepts without having a clear understanding of their meaning then confusion is likely to ensue. This article will define terms and concepts used in critical appraisal and provide examples of how they apply to the appraisal of studies in emergency medicine.

WHAT IS A HYPOTHESIS?

Research articles often describe testing a hypothesis and critical appraisal will often involve identifying what hypothesis has been tested. A hypothesis is a prediction. Having made a prediction, observation or experimentation is then used to determine whether the prediction is true. A hypothesis should be supported by theory. In other words, there should be a clear explanation of why we might expect the hypothesis to be true. If a hypothesis seems to have been plucked from thin air, without any supporting rationale, then we should be suspicious that it may have arisen by chance during analysis of the data.

WHAT ARE VALIDITY AND GENERALISABILITY?

Critical appraisal involves determining whether the findings of a research study are valid and generalisable. If the findings are likely to be true, then they are valid. If the findings are likely to apply to settings or situations outside the research study, then they are generalisable.

Validity  =  is this finding true?

Generalisability  =  is this finding applicable elsewhere?

There is obviously little point trying to generalise a finding that is not valid. So validity is usually considered before generalisability. Many would argue, however, that generalisability is equally important, because a finding that is only valid in one specific setting has as little practical use as a finding that is not valid. In practice, of course, validity and generalisability cannot be judged in simple yes/no terms but as degrees of validity and generalisability. …