*Last Edited: 3/18/2008*

## What does statistically significant mean?

In epidemiological studies, there is a need to quantify the extent to which random variability could produce results like those observed in a given study. Because these studies are based on a sample of people who are supposed to represent the population overall, factors such as the size of the group sampled will affect how often results like those seen could have occurred by chance. There are various tests that can be used to quantify how large this probability is. By convention, researchers often use a particular standard of 5% (or 1-in-20) as a guideline. Using this criterion, a finding would be called "statistically significant" if the probability of obtaining that observed result (or a more extreme one) is less than 1 in 20.