Often, a study’s level of precision is closely related to its size.
Why? You’ll remember that precision is made up of two elements – the number of things being averaged (or the sample size) and how much each individual element varies from the overall average (this is the variance of an individual item).
If you’re interested in the formula for precision, it looks like this-
Precision = N/S2
Where N = the Number of participants in the study, and S2= the variance (or the Standard deviation squared)
In most cases, studies have fairly similar variances, but the sample sizes of studies can be pretty different from each other. So, if you’re dividing the number of participants in each study by a very similar variance, the study size will have the most impact on your calculation of precision.