of outcomes, including differences in developmental changes in alcohol involvement. As recently discussed by researchers that have utilized similar methodology to study personality development (Johnson et al., 2007), the purpose of this statistical methodology is not to “carve nature at its joints” but rather provide an empirical framework for indentifying individual differences in the pattern of stability, change, and level of a given construct (e.g., impulsivity) across important developmental periods (e.g., emerging and young adulthood). As Johnson and colleagues (2007) note, once trajectory groups have been identified, the utility of the classes can be tested by examining the relations between group membership and important outcomes (e.g., alcohol use).
