In the case of physical and medical standards, a range of outcomes can be considered. And for some of them, the use of attrition appears warranted. Recruits with certain physical conditions, such as obesity or a very low level of physical fitness, may not be able to complete basic training or may not be able to adapt to difficult combat environments. Attrition might therefore be a reasonable outcome for evaluating specific standards for these conditions. The same might be said for such medical conditions as asthma, orthopedic disorders, and so forth.
Physical conditions such as obesity and fitness and medical conditions like orthopedic disorders can also be evaluated using performance outcomes of various types. For example, many military jobs may involve tasks that require minimum levels of strength, agility, or endurance. The advantage of using these types of performance outcomes is that screening devices might be designed that offer good predictive validity of the outcomes, such as the Assessment of Recruit Motivation and Strength test being tested by the Accessions Medical Standards Analysis and Research Activity (AMSARA).
Finally, another outcome that can be used for many physical and medical conditions is lost time on the job and the medical costs of injuries and sickness (including disability expenditures) arising from these conditions. The outcomes of lost time and medical costs may be especially appropriate for such physical conditions as obesity and fitness or such medical conditions as orthopedic disorders.
Given the selection of an appropriate outcome, the second step in a validity study is to establish a correlation or association between the physical or medical condition and the outcome. This usually requires an empirical study of some sort. The study may use existing military data, particularly when attrition rates are the outcome of interest. In other cases, an original prospective data collection effort may be required. The latter is usually necessary if the outcome is some type of job performance outcome that is not captured by military records.
Before discussing how a correlation is established empirically, it may be helpful to discuss the nature of this correlation and to understand approaches to validity assessments in various fields. In medical and some behavioral science research, the validity of a screening test is established by its effectiveness in detecting certain conditions (e.g., disease, impairment). Effectiveness of the screen is evaluated by several statistics, including sensitivity and specificity. These are illustrated using a two-by-two table (Table 3-1).