A quantitative condition which describes a process that is free of assignable/special causes of variation, e.g., variation in the central tendency and variance. Such a condition is most often evidenced on a control chart, i.e., a control chart which displays an absence of nonrandom variation.

A statistical technique used to eliminate variance in dependent variables caused by extraneous sources. In evaluation research, statistical controls are often used to control for possible variation due to selection bias by adjusting data for program and control group on relevant characteristics.

The process by which the variability of measurements or of data outputs of a system is controlled to the extent necessary to produce stable and reproducible results. To say that measurements are under statistical control means that there is statistical evidence that the critical variables in the measurement process are being controlled to such an extent that the system yields data that are reproducible within well-defined limits.

adjusting for the effects of confounded variables by statistically adjusting the value of the dependent variable for each treatment condition.

Is the condition of a process from which all special causes of variation have been eliminated and only common causes remain. Statistical control is evidenced on ,a control chart by the absence of points beyond the control limits and by the absence of any non-random patterns or trends.