ABSTRACT
Every research study is unique: It is carried out in a particular setting, using particular procedures, with a particular sample of participants, at a particular time. At the same time, studies are often conducted to determine general principles of behavior that are expected to operate in a variety of circumstances. An important question, therefore, is the extent to which the fi ndings from any one study apply in other settings, at other times, with different participants, when different procedures are used.
