04.06 Clinical Trial Design

There are a number of factors that make a good clinical trial design. There should be similarity of the control group, who do not receive the drug, with the group receiving the intervention (drug). Otherwise any difference between the control and intervention group, may be due to other differences between the groups, other than due to the drug intervention. One way of achieving similarity between groups is the random assignment of patients to control and intervention group. In initial clinical trials, the control group was untreated whereas the treated group were given the drug. This is almost guaranteed to show a beneficial effect with the drug, as people like to believe the drug is going to do them good. To avoid this, the control group are given an inert replica of the drug, which is known as the placebo. Placebos are very good for you! The placebo response (which means “I shall please”) is 40% of relief of pain in labour, and up to 60% in relieving depression. This is the key reason for not accepting anecdotal evidence, and requiring placebo-controlled clinical trials.

Another danger in clinical trials is observer bias. The observer of the patients will want the patient to get better and will be looking for signs of benefit with the drug, which may or may not be present. To avoid this problem, blinding is used. There are two types of blinding. In single blinded clinical trials, only the study participants are blinded, not the investigator, and this happens when it is considered important that the investigator knows which participant has the active drug. In double-blinded clinical trials, neither the participants nor the investigator know who is taking the active drug. The best design for a clinical trial is the randomized, double-blind, placebo-controlled trial. Such a trial has the highest likelihood of revealing the truth about the effects of a drug. The randomized, double-blind, placebo controlled trial has a very simple design (Figure 4.4).

Figure 4.4 Randomized, double-blind, placebo-controlled trial (Copyright QUT, Sheila Doggrell)

In a randomized, double-blind, placebo-controlled trial, the selected patient population is randomised to either the placebo (dummy tablet) or the drug, and the health of the participants is monitored.