Alcohol Use : Advantages and Disadvantages of Trajectory Approaches

by National Institute of Health

(Page 3 of 4)

Normative trajectory and multiple-trajectory approaches, both of which emphasize assessing the subjects' alcohol and other drug use at multiple times, have many advantages (as well as some disadvantages, primarily increased methodological and logistical complexity) compared with approaches that measure the subjects' drinking behavior only on one or two occasions. Both types of trajectory approaches, compared with one- and even two-time-point approaches, offer the potential for far greater understanding of the causes, developmental course, and consequences of the subjects' substance use. Identifying the course of the subjects' alcohol and other drug use across multiple measurement periods makes it possible to consider how people's substance use changes over time, together with other factors, and to better understand the risk factors for and consequences of different alcohol use patterns. This is especially important during adolescence and young adulthood, because people tend to experiment with alcohol and other drugs during this time, and substance use at a given time may have little relation to a young person's later patterns of use or abuse.

One important disadvantage of trajectory approaches is shared with all longitudinal studies: Participants with different characteristics and group memberships may drop out of the study at different rates.

A noteworthy limitation of both normative and multiple-trajectory approaches, compared with other longitudinal approaches, is that trajectory approaches traditionally tend to downplay day-to-day situational factors that may affect people's likelihood of drinking, such as negative mood or the peers a person is hanging out with on a specific day. In addition, such approaches tend not to focus on short-term consequences of alcohol use. To better identify and understand short-term fluctuations in alcohol use, some studies repeatedly measure subjects' behavior over short periods of time, for example using beepers or Web-based or paper diaries.

Importantly, methodological variations in different studies may contribute to different conclusions about alcohol use trajectories during the transition to adulthood. These include the operational definition of heavy drinking that is used, the characteristics of the sample such as age range or level of alcohol use, and the number of and interval between measurement occasions.

Normative and multiple-trajectory approaches each have distinct advantages and disadvantages, such that the advantage of one is the other's disadvantage. Researchers should determine which type of trajectory approach to use by the research questions they are addressing and the data characteristics they are using. Because normative approaches tend to be more straightforward and parsimonious than multiple-trajectory approaches, it is better to use a normative trajectory approach when the only difference among multiple-trajectory groups is the amount of substance use. As researchers have learned, however, the shapes of people's alcohol use trajectories often differ. This fact encourages the use of a multiple-trajectory approach that recognizes variability both across people and over time, rather than assuming homogeneity of the directions and rates of change within the entire population. This increased focus on identifying different developmental trajectories of alcohol use across adolescence and adulthood represents a major and welcome shift in researchers' ability to understand the meaning and course of alcohol use and problems across a person's life course. Advantages of the multiple-trajectory approach over the normative trajectory approach include being able to determine the specific risk and protective factors that apply to particular subgroups and being able to focus more on understanding the meaning of a person's behaviors in the context of his or her developmental history.

The multiple-trajectory approach also has important limitations. First, there is a danger that subgroups, identified as sets of tendencies and probable characteristics, may come to be seen as immutable, almost as diagnostic categories. This may be premature, because application of these analytic strategies to alcohol use trajectories is relatively new, and further research is needed to determine which subgroups will be found consistently across different samples and measures of alcohol use. Furthermore, the number of trajectory subgroups identified is logically dependent on the sample characteristics; the number, range, and spacing of observations; and the way variables are operationalized and measured.

Before findings derived from multiple-trajectory approaches can be translated into diagnostic tools, researchers need to have greater understanding about whether different risk factors can reliably distinguish different subgroups, either before members of these subgroups diverge from the normative pattern or during their divergence. Likewise, it is important to remember that a person's membership in a class or subgroup is probabilistic rather than absolute. Moreover, applied work using multiple-trajectory approaches to examine alcohol use patterns has tended not to emphasize variability among people within subgroups.

Finally, a noteworthy methodological limitation of multiple-trajectory approaches is that the range of ages included in a given study determines the study's ability to distinguish some subgroups from others. For example, studies that end when the subjects reach age 20 may inaccurately categorize some people as late-onset heavy drinkers, when instead they subsequently may reduce their drinking and therefore would be better described as fling drinkers. Similarly, because studies that begin in late adolescence lack data regarding alcohol use during early adolescence, they cannot distinguish decreasers from potential "early flings".

Predictors and Correlates of Trajectory Membership

Numerous longitudinal studies have examined predictors (typically measured early in the study) and outcomes of belonging to particular trajectory subgroups, such as role status or problem behaviors at or after the final assessment period used to identify the subgroups. Some of these, and their significance, are described in the following sections.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.