What is standard deviation in psychology?

The standard deviation is a measure of dispersion that shows how spread out the values in a data set are around the mean. It indicates the extent to which individual data points differ from the average. A smaller standard deviation means the data are closely clustered around the mean, while a larger one suggests greater variability. Because it is based on the original data, the standard deviation uses the same unit of measurement.

For example, in a psychology study recording participants' reaction times in seconds, the standard deviation would also be in seconds. A low standard deviation would indicate that most participants responded at similar speeds, whereas a high standard deviation would reflect more varied reaction times.