Aptitude-Treatment Interaction

There are countless illustrations in the social sciences of a description of a phenomenon existing for many years before it is labeled and systematized as a scientific concept. One such example is in Book II of Homer's Iliad, which presents an interesting account of the influence exerted by Agamemnon, king of Argos and commander of the Greeks in the Trojan War, on his army. In particular, Homer describes the behavior of Odysseus, a legendary king of Ithaca, and the behavior of Thersites, a commoner and rank-and-file soldier, as contrasting responses to Agamemnon's leadership and role as “the shepherd of the people.” Odysseus, Homer says, is “brilliant,” having “done excellent things by thousands,” while he describes Thersites as that “who knew within his head many words, but disorderly,” and “this thrower of words, this braggart.” Where the former admires the leadership of Agamemnon, accepts his code of honor, and responds to his request to keep the sage of Troy, the latter accuses Agamemnon of greed and promiscuity and demands a return to Sparta.

The observation that an intervention—educational, training, therapeutic, or organizational—when delivered the same way to different people might result in differentiated outcomes, was made a long time ago, as long as the eighth century BCE, as exemplified by Homer. In attempts to comprehend and explain this observation, researchers and practitioners have focused primarily on the concept of individual differences, looking for main effects that are attributable to concepts such as ability, personality, motivation, or attitude. When these inquiries started, early in the 20th century, not many parallel interventions were available. In short, the assumption at the time was that a student (a trainee in a workplace, a client in a clinical setting, or a soldier on a battlefield) possessed specific characteristics, such as Charles Spearman's g factor of intelligence, that could predict his or her success or failure in a training situation. However, this attempt to explain the success of an intervention by the characteristics of the intervenee was challenged by the appearance of multiple parallel interventions aimed at arriving at the same desired goal by [Page 41]employing various strategies and tactics. It turned out that there were no ubiquitous collections of individual characteristics that would always result in success in a situation. Moreover, as systems of intervention in education, work training in industry, and clinical fields developed, it became apparent that different interventions, although they might be focused on the same target (e.g., teaching children to read, training bank tellers to operate their stations, helping a client overcome depression, or preparing soldiers for combat), clearly worked differently for different people. It was then suggested that the presence of differential outcomes of the same intervention could be explained by aptitude-treatment interaction (ATI, sometimes also abbreviated as AxT), a concept that was introduced by Lee Cronbach in the second part of the 20th century.

ATI methodology was developed to coaccount both for the individual characteristics of the intervenee and the variations in the interventions while assessing the extent to which alternative forms of interventions might have differential outcomes as a function of the individual characteristics of the person to whom the intervention is being delivered. In other words, investigations of ATI have been designed to determine whether particular treatments can be selected or modified to optimally serve individuals possessing particular characteristics (i.e., ability, personality, motivation). Today, ATI is discussed in three different ways: as a concept, as a method for assessing interactions among person and situation variables, and as a framework for theories of aptitude and treatment.

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