Bridging the Gap: Microtrials and Idiographic Designs for Translating Basic Science into Effective Prevention of Substance Use

Power analysis for idiographic (within-subject) clinical trials: Implications for treatments of rare conditions and precision medicine

Power analysis informs a priori planning of behavioral and medical research, including for randomized clinical trials that are nomothetic (i.e., studies designed to infer results to the general population based on interindividual variabilities). Far fewer investigations and resources are available for power analysis of clinical trials that follow an idiographic approach, which emphasizes intraindividual variabilities between baseline (control) phase versus one or more treatment phases. We tested the impact on statistical power to detect treatment outcomes of four idiographic trial design factors that are under researchers' control, assuming a multiple baseline design: sample size, number of observations per participant, proportion of observations in the baseline phase, and competing statistical models (i.e., hierarchical modeling versus piecewise regression). We also tested the impact of four factors that are largely outside of researchers' control: population size, proportion of intraindividual variability due to residual error, treatment effect size, and form of outcomes during the treatment phase (phase jump versus gradual change). Monte Carlo simulations using all combinations of the factors were sampled with replacement from finite populations of 200, 1750, and 3500 participants. Analyses characterized the unique relative impact of each factor individually and all two-factor combinations, holding all others constant. Each factor impacted power, with the greatest impact being from larger treatment effect sizes, followed respectively by more observations per participant, larger samples, less residual variance, and the unexpected improvement in power associated with assigning closer to 50% of observations to the baseline phase. This study's techniques and R package better enable a priori rigorous design of idiographic clinical trials for rare diseases, precision medicine, and other small-sample studies.

Attachment Representation Moderates the Effectiveness of Behavioral Parent Training Techniques for Children with ADHD: Evidence from a Randomized Controlled Microtrial

Behavioral parent training is an evidence-based intervention for children with attention-deficit/hyperactivity disorder (ADHD), but knowledge on the differential effects of behavioral techniques for specific subgroups of children is very limited. Attachment representations of children with ADHD may affect how receptive children are to changes in parenting. In this study, we investigated whether specific behavioral techniques were more or less effective for children with ADHD in relation to their attachment representations. We included parents of 74 children with ADHD (4-11 years, M = 8.15) who took part in a larger randomized controlled microtrial in which they were randomized to a two session training in antecedent-based techniques (i.e., stimulus control techniques: rules, instructions; n = 26), a two session training in consequent-based techniques (i.e., contingency management techniques: praise, rewards, ignoring; n = 25) or a waitlist control condition (n = 23). We examined whether attachment representation moderated the effectiveness of a) training versus waitlist, and b) antecedent- versus consequent-based techniques. Attachment representations were measured with a story stem task, the intervention outcome was daily parent-rated problem behaviors of the children. Attachment representation did not moderate the effects of the training compared to the waitlist. However, compared to antecedent-based techniques, consequent-based techniques were less effective for more securely and less disorganized attached children, and particularly effective for more disorganized attached children. This was the first study examining attachment as a moderator of behavioral techniques for ADHD. If replicated, the findings of this study can be used for treatment development and tailoring.

Which Techniques Work in Behavioral Parent Training for Children with ADHD? A Randomized Controlled Microtrial

OBJECTIVE

Behavioral parent training (BPT) is an evidence-based intervention for children with attention-deficit/hyperactivity disorder (ADHD), but little is known about the effects of separate techniques parents learn in BPT.

METHOD

In a three-armed randomized controlled microtrial including parents of 92 children (4-12 years) with ADHD, we examined the efficacy of two sessions parent training involving either stimulus control techniques (antecedent-based condition (AC)) or contingency management techniques (consequent-based condition (CC)), compared to a waitlist. Primary outcome was daily parent-rated problem behaviors, secondary outcomes were parent-rated symptoms of ADHD and oppositional defiant disorder (ODD), and mental health-care consumption. Measures were completed at baseline (T0), immediately after the training (T1), at two weeks (T2) and three months (T3) follow-up. We also explored whether child and parent characteristics moderated treatment effects.

RESULTS

Compared to the waitlist, in the AC, daily rated problem behaviors improved at T1 (d= .56) and T2 (d= .65); in the CC, these behaviors only improved at T2 (d= .53). Daily rated problem behaviors within both conditions remained stable between T2 and T3. In the AC compared to the other conditions, inattention symptoms decreased at T1 and T2. For both active conditions compared to waitlist, hyperactivity-impulsivity symptoms decreased only at T2 and ODD symptoms did not decrease. No moderators were identified. Mental health-care consumption after training was low and did not differ between the active conditions.

CONCLUSIONS

Brief training of parents in antecedent- or consequent-based techniques improves problem behaviors of children with ADHD. Antecedent-based techniques appear to be especially important to target inattention.

Effectiveness of Specific Techniques in Behavioral Teacher Training for Childhood ADHD: A Randomized Controlled Microtrial

Objective: Behavioral teacher training is the most effective classroom-based intervention for children with attention-deficit/hyperactivity disorder (ADHD). However, it is currently unknown which components of this intervention add to its effectiveness and for whom these are effective.

Method: In this microtrial, teachers of 90 children with impairing levels of ADHD symptoms (6–12 years) were randomly assigned to one of three conditions: a short (2 sessions), individualized intervention consisting of either (A) antecedent-based techniques (stimulus control), (B) consequent-based techniques (contingency management) or (C) waitlist. Primary outcome was the average of five daily assessments of four individualized problem behaviors, assessed pre and post intervention and three months later. Moderation analyses were conducted to generate hypotheses on child, teacher and classroom factors that may contribute to technique effectiveness.

Results: Multilevel analyses showed that both antecedent- and consequent-based techniques were equally and highly effective in reducing problem behaviors compared to the control condition (Cohen’s d =.9); effects remained stable up to three months later. Child’s age and class size were moderators of technique effectiveness. For younger children, consequent-based techniques were more effective than antecedent-based techniques, whereas for older children the effect was in the opposite direction. Further, beneficial effects of antecedent-based techniques increased when the number of students per class decreased, whilst effectiveness of consequent-based techniques did not depend on class size.

Conclusions: This study shows that both antecedent- and consequent-based techniques are highly effective in reducing problem behavior of children with ADHD. Interventions may be adapted to the child’s age and class size.

Using baseline target moderation to guide decisions on adapting prevention programs

Tom Dishion, a pioneer in prevention science, was one of the first to recognize the importance of adapting interventions to the needs of individual families. Building towards this goal, we suggest that prevention trials be used to assess baseline target moderated mediation (BTMM), where preventive intervention effects are mediated through change in specific targets, and the resulting effect varies across baseline levels of the target. Four forms of BTMM found in recent trials are discussed including compensatory, rich-get-richer, crossover, and differential iatrogenic effects. A strategy for evaluating meaningful preventive effects is presented based on preventive thresholds for diagnostic conditions, midpoint targets and proximal risk or protective mechanisms. Methods are described for using the results from BTMM analyses of these thresholds to estimate indices of intervention risk reduction or increase as they vary over baseline target levels, and potential cut points are presented for identifying subgroups that would benefit from program adaptation because of weak or potentially iatrogenic program effects. Simulated data are used to illustrate curves for the four forms of BTMM effects and how implications for adaptation change when untreated control group outcomes also vary over baseline target levels.