 Proponents of EBM regard RCTs as reliable means to judge treatment efficacy because they can help to control for a variety of (though not all) biases and confounders. If, for instance, the symptoms of a patient or group of patients improve after an intervention, this may be due to spontaneous remission rather than the treatment. An experimental design that compares a treatment group with one or several control groups is therefore better able to control for this confounder than a simple “before-and-after” design. Similarly, a design in which the allocation to treatment and control groups is done by a non-random process, it is possible that healthier patients end up in the treatment and less healthy patients in the control group. If so, the measured improvement may be due to the health status of the patients rather than the intervention. Especially if the allocation is done by a medical researcher who has a stake in the matter (for instance because she has developed the new treatment), allocation decisions may consciously or subconsciously be influenced by expectations about who will profit from the intervention and thus create unbalanced groups. Allocation by a random process helps to control this source of bias.