Take a drug and alcohol prevention program that’s been proven to work. Take a second program that aims to help young people spend their leisure time constructively. It’s not so surprising that young people exposed to high levels of these interventions do better than those with no exposure.

But what if an intervention can’t be implemented fully? Surely a little exposure to a good intervention is better than none? A new study shows that, contrary to expectations, youth who received a low dosage of two proven interventions ended up using drugs and alcohol more than children in the control group who received no intervention. Just like many medicines, the wrong dosage of an evidence-based intervention may not only have a null effect, it may even be more harmful than not receiving it in the first place.

In short, dosage matters.

A new attention to implementation and dosage
The attention to dosage is part of the sea-change that has occurred in prevention science over the last decade. It has increasingly been demonstrated that the quality of implementation of evidence-based programs is critical to their effectiveness at improving child outcomes. This rising tide has lifted all boats - implementation quality is now routinely incorporated into evaluations of interventions for children and youth.

“Dosage” is one important dimension of implementation quality. Depending on the type of intervention, dosage may refer to the time spent in an intervention session, the number of sessions, or the overall duration of the program. Dosage is thus distinct from other components of implementation quality, such as fidelity to the core model or the quality of training received by program deliverers.

A team of American and Swedish researchers set out to test how dosage affects the outcomes of evidence-based programs. Laura Ferrer-Wreder from Stockholm University, Sweden, Hans Saint-Eloi Cadely from Auburn University in the US, and colleagues undertook an experimental evaluation of a combination of two interventions designed to reduce drug and alcohol use of children in middle and high schools in the US.

The first intervention in the double act was Life Skills Training (LST), a widely implemented curriculum-based intervention proven by multiple randomized control trials to reduce drug and alcohol use. It seeks to promote resistance and self-regulation skills, and aims to help children make healthy choices and realize the impact of their actions on others.

The second intervention was TimeWise: Taking Charge of Leisure Time. Rather than focusing on reducing risks for drug and alcohol use, this intervention is largely focused on health enhancement by promoting healthy leisure time activities and prosocial behavior and alleviating boredom in children’s spare time. The combination of LST and TimeWise was proposed by the researchers to be “complementary yet distinct, thereby yielding a potentially potent combination that would be novel for participating youth.”

Dosage was assessed as a combination of the amount of prevention curriculum covered by teachers, and the number of prevention classes students attended. Children receiving interventions were split into high and low dosage groups.

The team measured a number of intermediate outcomes hypothesized to precede reductions in drug and alcohol use. These included assertiveness, anxiety control, motivation to participate in prosocial leisure activities and intention to use. Although changes in actual drug and alcohol use were not expected until at least the second or third year following intervention, these outcomes were measured at the one-year follow-up. Outcomes of 250 children receiving both interventions were compared to outcomes of 465 children in a matched control group that did not receive any intervention.

So what did they find? Overall, irrespective of dosage, children receiving the interventions showed improvements in relation to anxiety and prosocial leisure-time activity compared to the control group, although no effects were observed in relation into actual drug and alcohol use. Follow-ups are underway to assess whether improvements in drug and alcohol outcomes will be observed at two or three years, as is typical.

Too much or too little?
What about dosage? Is the amount of exposure to an intervention related to outcomes? This is where it gets really interesting.

As expected, the positive impacts of intervention were more pronounced for children who received a high dosage. These children receiving more intervention sessions not only showed even greater improvements in anxiety and prosocial leisure-time activity than those receiving a low dosage, they also showed improvements in assertiveness and lower intention to use drugs and alcohol.

But the really striking finding is that children who received a low dosage of the intervention ended up using drugs and alcohol more than children in the control group who received no intervention. Just like many medicines, the wrong dosage of an evidence-based intervention may not only have a null effect, it may even be more harmful than not receiving it in the first place.

Poor implementation and the wrong dosage of evidence-based interventions therefore have the potential to do more harm than good. Well-intended interventions, if poorly implemented, can be dangerous.

References
Ferrer-Wreder, Laura, Hans Saint-Eloi Cadely, Celene E. Domitrovich, Meg L. Small, Linda L. Caldwell, Michael J. Cleveland. 2010. “Is More Better? Outcome and Dose of a Universal Drug Prevention Effectiveness Trial.” Journal of Primary Prevention 31: 349-363.