| The number of individual scores that can vary without changing the sample mean. Statistically written as 'N-1' where N represents the number of subjects. | |
| Samples in which informants provide contact information about other people who share some of the characteristics necessary for a study | |
| A graphed cluster of dots, each of which represents the values of two variables | |
| Bias introduced to a sample when a large fraction of those sampled fails to respond. |