Therefore, researchers use retention or transfer tests (the latter involve a variation of what was practised) that are performed after a certain time interval (i.e. at least 1 day, but sometimes several days or even weeks). The purpose of this interval is to allow any temporary performance-enhancing effects (such as caused by greater guidance) or performance-degrad- ing effects (such as caused by increased fatigue) that certain practice conditions may have created to dissipate, leaving only the relatively permanent, or learning, effects.