Planning for Long-Term Follow-Up: Strategies Learned from Longitudinal Studies

Abstract

Preventive interventions are often designed and tested with the immediate program period in mind, and little thought that the intervention sample might be followed up for years or even decades beyond the initial trial. However, depending on the type of intervention and the nature of the outcomes, long-term follow-up may well be appropriate. The advantages of long-term follow-up of preventive interventions are discussed and include the capacity to examine program effects across multiple later life outcomes, the ability to examine the etiological processes involved in the development of the outcomes of interest, and the ability to provide more concrete estimates of the relative benefits and costs of an intervention. In addition, researchers have identified potential methodological risks of long-term follow-up such as inflation of type 1 error through post hoc selection of outcomes, selection bias, and problems stemming from attrition over time. The present paper presents a set of seven recommendations for the design or evaluation of studies for potential long-term follow-up organized under four areas: Intervention Logic Model, Developmental Theory and Measurement Issues; Design for Retention; Dealing with Missing Data; and Unique Considerations for Intervention Studies. These recommendations include conceptual considerations in the design of a study, pragmatic concerns in the design and implementation of the data collection for long-term follow-up, as well as criteria to be considered for the evaluation of an existing intervention for potential for long-term follow-up. Concrete examples from existing intervention studies that have been followed up over the long term are provided.

Keywords: Assessment design; Developmental; Follow-up; Intervention; Longitudinal; Retention.

Figure 1

Intervention Logic Model. The intervention logic model specifies the theoretical mechanisms through which the intervention is expected to influence target outcomes. It consists of an action theory reflecting how the treatment will affect known antecedents of the target outcomes, and a conceptual theory drawn from etiological findings on what mediators are known to be related to the outcomes of interest. The developmental theory then specifies how these intervention consequences may unfold over time (see figure 2).

Figure 2

Illustration of a developmentally-specified intervention logic model.