Helping people to stick to allocated treatments
Differences between intended and actual treatments during treatment comparisons can happen in other ways that may complicate the interpretation of tests of treatments.
Participants in research should not be denied medically necessary treatments. When a new treatment with hoped-for, but unproven, beneficial effects is being studied in a fair test, therefore, participating patients should be assured that they will all receive established effective treatments.
If people know who is getting what in a study, several possible biases arise. One is that patients and doctors may feel that people allocated to ‘new’ treatments have been lucky, and this may cause them unconsciously to exaggerate the benefits of these treatments. On the other hand, patients and doctors may feel that people allocated ‘older’ treatments are hard done by, and this disappointment may cause them to under-estimate any positive effects.
Knowing which treatments have been allocated may also cause doctors to give the patients who have been allocated the older treatments some extra treatment or care, to compensate, as it were, for the fact that they had not been allocated to receive the newer, but unproven treatments.
Using such additional treatments in patients in one of the comparison groups but not in the other group complicates the evaluation of a new treatment, and risks making the comparison unfair and the results misleading. A way to reduce differences between intended and actual treatment comparisons is to try to make the newer and older treatments being compared look, taste and smell the same.
This is what is done when a treatment with hoped-for beneficial effects is compared with a treatment with no active ingredients (a sham treatment, or placebo), which is designed to look, smell, taste and feel like the ‘real’ treatment. This is called ‘blinding’, or ‘masking.’
If this ‘blinding’ can be achieved (and there are many circumstances in which it cannot), patients in the two comparison groups will tend to differ in only one respect – whether they have been allocated to take the new treatment or the one with no active ingredients. Similarly, the health professionals caring for the patients will be less likely to be able to tell whether their patients have received the new treatment or not. If neither doctors nor patients know which treatment is being given, the trial is called ‘double blind’.
As a result, patients in the two comparison groups will be similarly motivated to stick to the treatments to which they have been allocated, and the clinicians looking after them will be more likely to treat all the patients in the same way.