What researchers mean by... effectiveness

If a drug or exercise reduces pain and disability, if a vaccine protects us from infection, if talking to a therapist relieves our depression, we judge the intervention to be “effective.” When it comes to health and illness, most people understand this basic concept of effectiveness.

Research in workplace health is often undertaken to determine the effectiveness of interventions to protect or improve the health of workers. For example, will ergonomic programs reduce or prevent repetitive strain injury among keyboard operators? Does safety training reduce injuries in young workers?

A health service or intervention is considered to be “effective” if well-designed studies show that it improved health outcomes in a typical community or workplace setting.

But there's a big difference between effectiveness (how well a particular health service or intervention can be expected to work in the real world) and efficacy — how well it works in the ideal, controlled environment of a formal research study.

Researchers who study efficacy often do so in the context of a randomized controlled trial or RCT. In this type of study, subjects are randomly assigned to an intervention group (those who receive the experimental treatment or service) or a control group (those who don't). During the course of a RCT, subjects are closely monitored and are expected to adhere to often complex treatment regimens. Their progress may be followed by researchers for weeks, months or even years after the trial ends.

Just because an intervention scores high on efficacy during a research trial, that's no guarantee it will be effective in the real world. One reason is that, outside the ideal setting of a clinical trial or intervention study, people don't always comply with directions about prevention or treatment, and there is usually no follow-up to see how well they do over time.

Because questions about efficacy and effectiveness are often so complex, a new generation of research has started to evolve. It analyzes the effectiveness of interventions that have been found to work well in a controlled setting and also measures how successfully they transfer to the real world.

In many cases, however, research will establish that several interventions are effective in treating an illness or preventing injury. When this happens, decision-makers must weigh the effectiveness with other important considerations. For example:

  • Even if the intervention is shown to be effective, how large was the effect? Did the intervention make a small difference in preventing or successfully treating a relatively rare event or complication? Or did it make a large difference in preventing or treating an extremely common problem?
  • Is the effective treatment or intervention available and affordable? If not, are there any reasonable alternatives?
  • Did the research show any adverse effects that might have been caused by the intervention or treatment? If so, did these outweigh the benefits?

How important is effectiveness? Those who use research results — for example, patients and workers, health-care providers, employers, organized labour and policy-makers — want to know whether a particular intervention for relieving low-back pain or reducing on-the-job accidents is effective. Knowing that an intervention is clearly not effective or is no more effective than other strategies can also be extremely useful.

Source: At Work, Issue 39, Winter 2005: Institute for Work & Health, Toronto