# Precision

Precision is a term that can have slightly different meanings, depending on the context in which it is used. Some would argue that what we should be talking about is **imprecision** - the propensity of any series of measurements to get different answers. If we measure the same thing in the same (or different) ways, we expect to get the same answer. Often we do not. Here are some definitions:

- A measure of the closeness of a series of measurements of the same material. In laboratories precision is expresses as a
**coefficient of variation**, which is nothing more than the standard deviation divided by the mean and expressed as a percentage. - A measure of the likelihood of random errors in the results of a study, meta-analysis or measurement. Confidence intervals around the estimate of effect from each study are a measure of precision, and the weight given to the results of each study in a meta-analysis (typically the inverse of the variance of the estimate of effect) is a measure of precision (i.e. the degree to which a study influences the overall estimate of effect in a meta-analysis is determined by the precision of its estimate of effect). [Note: faked studies are often very precise, and can be given disproportionate weight in meta-analysis. Very great precision is not a feature of biological systems, and should be looked at with a cold and fishy eye.]
- The proportion of relevant citations located using a specific search strategy, i.e. the number of relevant studies meeting the inclusion criteria for a trials register or a review) divided by the total number of citations retrieved.