single value that tells us how far scores deviate (move away) from the mean. It is used with the mean.
The larger the SD, the greater the dispersion/spread within a set of data. A large SD suggests that not all ppts were affected by the IV.
A low standard deviation is better as it means that the data are tightly clustered around the mean, suggesting ppts responded in a similar way and the results are more reliable.
Strengths
This is a much more precise measure than the range as it includes all values.
