SELECTING CONTROL GROUPS: SAMPLE CASE OF COGNITIVE INTERVENTION TRIALS
Over the past two decades, there has been steadily growing interest in the development and testing of cognitive interventions for older adults to prevent cognitive decline and improve daily functioning and overall personal well-being (Gates, Sachdev, Fiatarone Singh, & Valenzuela, 2011; Gross, Parisi, et al., 2012; Stine- Morrow & Basak, 2011). For example, the Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE) study was a large multi-site clinical trial of a cognitive intervention for community-dwelling older adults (Jobe et al., 2001; Rebok et al., 2014). ACTIVE was a randomized, controlled, single-masked trial using a four-group design consisting of three treatment arms and a no-contact control group (see Figure 8.1). Each treatment arm included ten 60- to 75-minute training sessions for one of three cognitive abilities (memory, reasoning, and attentional processing speed) thought to underlie everyday functional capacity. Assessors were masked to participant treatment assignment. Training exposure and social contact were standardized across the three interventions so that each intervention could serve as a social contact control for the other interventions. As described by Jobe et al. (2001, p. 456), the design allowed for testing of both social contact effects, as represented in the dashed lines in Figure 8.1 (via the contact control groups) and retest effects (via the no-contact control group) on outcomes. Being able to assess
Figure 8.1 Hypothesized mode of effects in the ACTIVE trial.
Source: Jobe et al. (2001). ADL = activities of daily living; IADL = instrumental activities of daily living.
retest effects is an important advantage of a no-treatment or no-contact control in cognitive intervention research because the magnitude of practice effects may be substantial (Gross, Inouye, et al., 2012; Willis, 2001). Simply becoming familiar with the cognitive tests being administered and the testing routine can lead to significant improvement even without specific intervention.
The choice of an appropriate control group was a key issue in the development of the protocol for the ACTIVE trial (Jobe et al., 2001). There is no pharmacologic treatment or other usual care for normal older adults for cognitive performance. Therefore, usual care could be considered to be no care and thus no-contact was considered to be the equivalent control group to usual care. Moreover, previous investigations of cognitive training and occupational therapy interventions to improve functioning showed that a no-contact control group does not differ from a placebo social-contact group (Clark et al., 1997; Willis, Cornelius, Blow, & Baltes, 1983). One of the most elegant features of ACTIVE was that the design of the trial allowed multiple estimates of the nontreatment effects on the targeted abilities by estimating the influence of each training intervention (e.g., memory) on nontrained abilities relevant to the other two interventions (e.g., reasoning, attentional processing speed). The high degree of specificity of the effects reported given this design (e.g., see Ball et al., 2002; Willis et al., 2006) suggests that the generalized expectancy of doing well does not in itself play an important role in improving cognitive performance in the absence of target-specific training (Stine-Morrow & Basak, 2011).
In contrast to intervention trials such as ACTIVE that target specific cognitive skills or abilities, an alternative approach to intervention involves nonspecific stimulation of cognitive function via engagement in everyday stimulating cognitive, physical, and social activities (Fried et al., 2013; Park et al., 2013; Stine-Morrow et al., 2014). These stimulation/engagement approaches introduce special challenges when selecting appropriate controls. An example of an engagement model of cognitive intervention can be seen in the Baltimore Experience Corps trial (Fried et al., 2013). The Experience Corps® (EC) program is an innovative, community-based model for health promotion for older adults (Fried et al., 2004, 2013; Rebok et al., 2011) that involves volunteers aged 60 and older working with low-income, urban schools as mentors of children in grades K-3 for 15 hours a week throughout 2 academic school years. The program seeks to create meaningful, socially valued roles for older adults while simultaneously serving as a vehicle for health promotion by encouraging greater cognitive, physical, and social activity—all factors that have been shown to promote greater health and well-being and enhance cognitive fitness. The underlying two goals are to create a more active and healthier older population by engaging them in activities that can make a difference in society; and a student population having more educational needs met. A secondary benefit of Experience Corps design was the enhanced ability to create a positive learning environment in the classroom that results in schools having stronger academic performance.
An intention-to-treat, randomized, controlled effectiveness trial of the Experience Corps program recruited adults 60 and older who were eligible and randomized them to the intervention, Experience Corps participation, or to a usual volunteering opportunity, wait-list control (Fried et al., 2013). Those randomized to Experience Corps were assigned to serve for at least 1 year in a public elementary school, with grades Kindergarten through the third grade. Older adults randomized to the control arm were referred to the Baltimore City Commission on Aging and Retirement Education (CARE), where usual volunteer opportunities in Baltimore City, other than Experience Corps, were offered; these were selected to be of short duration and/or low time demand, such as volunteering at health fairs, city festivals, and senior center events. This was a usual care, low-activity control that was deemed more credible than a no-contact control because many older adults volunteer on their own, but usually for only a few hours a week and often for only limited periods of time. Those in the control arm were wait-listed for participation in Experience Corps after 2 years, should they remain interested. This proved to be a challenge as a few participants assigned to the control arm were not content to wait that long and tried to join the Experience Corps program without actually participating in the study. We also found that surprisingly few of the controls (about 20%) were actually still interested in joining the program after waiting 2 years, suggesting that their motivation or ability to participate may have decreased over time, or they may have found alternative volunteering opportunities.
As part of the Experience Corps trial, we also initially planned to randomize schools either to receive Experience Corps or to control status. Although randomization of schools was the gold standard to which we aspired, political realities made it impossible to randomize. For example, the city government wanted to select certain schools for participation on the basis of the level of educational need or political considerations. To maximize inference validity, we therefore identified control schools via a propensity score matching approach (Fried et al., 2013). Thus, it may not always be possible or feasible to carry out fully randomized trials in the complex environment of the real-world.
In a recent multimodal intervention study, Park and her colleagues used novel, real-world activities, which offer a degree of challenge and stimulation that can increase alongside increasing expertise (Park & Bischof, 2013). In their Synapse Project, a supported activity intervention, participants engaged in a new cognitively stimulating activity (i.e., quilting, digital photography, or both activities) for about 15 hours per week for 3 months (Park et al., 2013). The three intervention groups were compared to one of three control arms (social control, placebo, and notreatment) over the 3 months. The social control group engaged in nonintellectual activities such as field trips and entertainment and socialized for 15 hours per week. In the placebo control condition, participants worked on cognitive tasks that relied on previous knowledge and did not require active learning. No-treatment controls were required to complete only a weekly checklist of their daily activities. The use of multiple controls in this study was important in helping the investigators isolate the effects of different types of activity. However, this advantage needs to be weighed against the increased costs of including multiple control groups and the need to recruit and assess more participants.