This is a way of controlling for the effects of extraneous/confounding variables. Allocating participants to tasks, selecting samples and so on, should be left to chance as far as possible, to reduce the investigator’s influence on a study.
Standardisation:
This is where the experience of an experiment is (as far as possible) kept identical for every participant, for example using standardised instructions. This reduces the effect of extraneous/confounding variables.
