Randomized control clinical trial studies

This trial design, which is the most scientifically desirable, involves randomly assigning participants into either control or test groups, with concurrent testing of both groups. (Randomness means that each participant has an equal chance of being assigned to one or the other group. This can be achieved by, for example, flipping a coin or drawing names from a hat). Randomness is important as it:

• removes the potential for bias (conscious or subconscious) and, thus, will produce comparable groups in most cases;

• guarantees the validity of subsequent statistical analysis of trial results.

The trial may also be unblinded or blinded. In an unblinded ('open') trial, both the investigators and participants know to which group any individual has been assigned. In a single blind trial, only the investigator is privy to this information, whereas neither the investigator nor the participants in double blind trials know to which group any individual is assigned. Obviously, the more blind the trial, the less scope for systematic error introduced by bias.

The most significant objection to the randomized control design is an ethical one. If a new drug is believed to be beneficial, then many feel it is ethically unsound to effectively deprive up to half the trial participants from receiving the drug.

One modification that overcomes the ethical difficulties is the use of historical control trials. In this instance, all the trial participants are administered the new drug and the results are compared with previously run trials in which a comparable group of participants was used. The control data are thus obtained from previously published or unpublished trial results. This trial design is non-randomized and non-concurrent. Although it bypasses ethical difficulties associated with withholding the new drug from any participant, it is vulnerable to bias. The trial designers have no influence over the criteria set for their control group. Furthermore, historical data can distort the result, as beneficial responses in the test subjects may be due not only to the therapeutic intervention, but generally improved patient management practices. This can be particularly serious if the control data are old (in some trials it was obtained 10-20 years previously).

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