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Design of Trials
Phase 3 effectiveness trials are essentially experiments during which researchers compare the clinical course of women who use an experimental product with those who do not.
To make sure that any observed differences between the two groups are due to the experimental product and not other factors, scientists use a process called randomisation that assigns women by chance to either an "experimental group" or a "control group." Randomisation ensures that any differences among women --other than those that result from use of the product-- are equally distributed between the two groups. This is called "eliminating bias."
In microbicide trials, both the experimental and control groups would be treated for STIs and given access to free condoms and actively encouraged to use them at every act of intercourse. Women in the experimental group would also be instructed to use the experimental microbicide in addition to condoms every time they had sex, or the experimental product alone if condom use was not possible. Women in the control group would receive the same instructions but would be given a placebo product, fashioned to look and feel like the experimental microbicide but without active ingredients. In a "blinded" controlled trial, neither the participants nor the scientists know which group is which until the end of the trial.
Scientists would follow the women over the course of the study, observing the number of STI and HIV infections that developed in both groups. Using statistical analysis, researchers would then determine whether there were fewer infections among women who used the experimental product than among those who did not. If so, and if the result were greater than chance (i.e., statistically significant), the product could be said to reduce infection.
