The results of all psychological experiments are noise degraded to some degree. In fact, I’d say that the problem of noise-degraded data is the single most important problem facing modern psychology. Noise-degradation has no respect for discipline, philosophy, or methodology - it affects most measurements including both physical and psychological. It occurs

· when representing real numbers (e.g., reaction time) on a computer due to finite-length registers,
· from uncontrolled environmental factors,
· because most measuring devices do not have perfect resolution or accuracy,
· from subjects being inconsistent in their responses to the same stimulus,
· and it occurs when we use only a small sample of stimuli from the total stimulus set.

One way to remove variability in psychophysical data has been to replicate the experiment using the same stimulus set then use statistical procedures to remove the error.