Full Answer Section

A spurious relationship is a correlation between two variables that is caused by a third, unmeasured variable. In this case, a third variable that could explain the correlation between pain aides and headache reduction is the placebo effect.

The placebo effect is a phenomenon in which people experience a benefit after receiving a placebo, even though the placebo does not contain any active ingredients.

The placebo effect is thought to be caused by the power of suggestion. When people believe that they are receiving a treatment that will be effective, they are more likely to experience a benefit from that treatment, even if the treatment itself is ineffective.

In the experiment described, it is possible that the group that received pain aides experienced a greater reduction in headaches simply because they believed that the pain aides would be effective.

To determine whether or not causality was established in this experiment, it would be necessary to conduct a further experiment that controlled for the placebo effect. One way to do this would be to use a double-blind design.

In a double-blind design, neither the participants nor the researchers know who is receiving the pain aides and who is receiving the placebo. This helps to eliminate the placebo effect as a possible explanation for the results.

If a double-blind experiment were to show that the pain aides group had a greater reduction in headaches than the placebo group, then this would provide more convincing evidence that the pain aides were causing the reduction in headaches.