Practitioner effect. The practitioner’s style of practice influences outcomes, so different practitioners applying the same intervention may have different effects to some degree. Example: Arnold had...

Practitioner effect. The practitioner’s style of practice influences outcomes, so different practitioners applying the same intervention may have different effects to some degree. Example: Arnold had been substitute teaching on many occasions over several years in Marie’s class and knew her course materials quite well. However, when he had to take over her class on a permanent basis because she resigned with a serious illness, he was surprised that he wasn’t as effective in teaching her class as Marie had been.