WHEN AND WHY TO INCLUDE A CONTROL GROUP

Choosing an appropriate control group or condition(s) is always a critical decision in developing and evaluating a behavioral intervention and is most important when designing an RCT. Experimental research on psychological and behavioral interventions is usually implemented across a number of phases (Gitlin, 2013; Mohr et al., 2009; Schwartz, Chesney, Irvine, & Keefe, 1997). In thinking about control conditions, the investigator needs to consider the phase of intervention development: Phases I, II, III, IV, V, VI, and VII (see Table 8.1). Phase I trials are feasibility trials focused on developing and pretesting the acceptability, feasibility, and safety of the intervention components and development of the intervention manual. No control condition is needed. The second phase is exploratory and involves determining the frequency, duration, and intensity of a specific treatment intervention and defining the relevant outcomes. In this phase, the investigator would compare various doses of the intervention in order to determine the optimal frequency of contact or duration of treatment. The third phase would evaluate the efficacy of the intervention compared to the current standard treatment, or to usual care treatment if no standard of care or current best practice exists. A Phase III trial might also compare two common behavioral interventions that involve different assumptions about the mechanisms of action and likely outcomes (Schwartz et al., 1997). These trials typically include participants with comorbidities and multiple sites (Mohr et al., 2009). Phase IV studies are effectiveness trials that evaluate the transportability of the intervention to real-world settings. Phase IV trials may use a quasi-experimental design (e.g., case control) to evaluate the effect of a behavioral intervention in a health care setting where patients self-select to receive a particular intervention (Schwartz et al., 1997). In such cases, the investigator may need to statistically adjust for pretreatment differences between the cases and controls (e.g., socioeconomic status (SES) or preexisting medical conditions). In Phase V, most translational studies (see

TABLE 8.1 Suggested Control Conditions for Different RCT Phases

Phase

Objectives

Suggested Control Conditions

I

Develop and pretest intervention feasibility

None

II

Determine appropriate frequency, duration, and intensity; define relevant outcomes

Compare various doses of intervention

III

Evaluate efficacy of intervention as compared with standard treatment

Compare new treatment to standard

IV

Confirm effectiveness of intervention in "real-world" setting

Case control in clinical setting where participants self-select for intervention

V

Put intervention into practice, evaluate fidelity, test strategies for increasing reach, adoption

Compare effectiveness of different implementation strategies

VI

Distribute information about an intervention, scale up, translate for widespread diffusion

None

VII

Institutionalize an intervention program, policy, or practice

None

Note: Phases I—IV describe the traditional four-phase sequence for developing an intervention; phases V-VII have been added for translating, implementing, and institutionalizing the intervention (see Gitlin, 2013). Source: Adapted from Schwartz et al. (1997).

Gitlin, Marx, Stanley, & Hodgson, 2015) use a pre-post design and do not include a control group. However, implementation studies can include a comparison group when the goal is to compare the effectiveness of different implementation strategies. The use of control groups in subsequent phases for the advancement of an intervention (Phase VI—diffusion/dissemination; and Phase VII—sustainability) is uncharted at this point, but it seems unlikely that control conditions are necessary.

Thus, control conditions are most important when evaluating the efficacy or effectiveness of behavioral interventions. The efficacy or the effectiveness of behavioral interventions is always determined relative to a control condition (Mohr et al., 2009). Efficacy, or “explanatory,” trials usually precede effectiveness studies (also known as “pragmatic” studies) and refer to those trials conducted under optimal and controlled experimental conditions, whereas effectiveness trials are RCTs carried out in routine, “real-world” conditions. Because efficacy trials are aimed at determining the benefits of intervention for a specific group, they are necessary but not sufficient for establishing the effectiveness of interventions (Melnyk & Morrison-Beedy, 2012). However, the distinction between the two types of trials is a continuum rather than a dichotomy, and pure efficacy trials or pure effectiveness trials likely do not exist (Singal, Higgins, & Waljee, 2014).

 
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