Withhold Treatment Waiting List Control Groups

Yet another proposal, one consistent with RCT methodology but still questionable, is to randomly assign patients either to the T group or to a waiting list control group. Those in the waiting list control group are asked to refrain from seeking treatment for their disorder for the duration of the RCT, at the end of which they are given T if they then wish to receive it.

There is an ethical problem here. Patients being recruited into an RCT suffer from some disorder for which they seek help. It is difficult in many cases for clinical researchers to maintain clinical equipoise —defined as "a state of genuine uncertainty on the part of the clinical investigator regarding the comparative therapeutic merits of each arm in a trial" (Freedman 1987)—when the choices are between using a treatment that has a rationale, and for which there is justification for a belief that it might be helpful, and denying treatment for the duration of the study. Clinical equipoise is not solely an issue related to ethics. Lack of clinical equipoise often has repercussions for the scientific validity of the RCT, because when researchers are sure that T is better than the selected C, it is difficult to ensure the scientific objectivity necessary to the design, conduct, and analysis of the trial in order to produce a balanced and fair comparison of T versus C.

Clearly, if the disorder that the patients have is not serious, disabling, or painful; if it is unlikely to worsen with a delay in treatment; and particularly if no treatments are available for the condition outside the RCT that the patients would have had access to had they not been in the RCT, there is no convincing ethical argument for withholding treatment. However, it is not the ethical considerations but rather practical considerations that make the choice of withholding treatment untenable.

When patients seeking help for a disorder are able to obtain treatment from clinicians in their community, patients are less likely to volunteer for an RCT in which they take a chance of having such help withheld. Thus, the sample that is recruited into an RCT with a waiting list control group is likely to be nonrepresentative of the population with the disorder, often missing adequate representation of those most seriously affected by the disorder and those most anxious to be relieved of the effects of the disorder.

Moreover, after randomization, patients in the control group are more likely to drop out to seek outside help, introducing bias to the RCT and loss of power. Indeed, in many cases, clinicians observing patients in the waiting list control group often relent and transfer patients from the control group to treatment group prior to the end of the RCT, because of clinical ethical concerns.

Technically, this is a valid RCT proposal, because there is a C (in this case, temporary withholding of treatment) and randomization to T and C groups. However, in waiting list-controlled RCTs, it is very difficult to blind assessment of the outcomes. Patients are often very aware that they are receiving no treatment for their disorder and such awareness can color all measures of response. Consequently, the problems of sample bias, measurement bias, missing data, dropouts, loss of power, and bias in resulting effect sizes militate against choosing a waiting list control group in most cases.

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