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Thread: Some Important Concepts about Clinical Trials

  1. #1
    PharmD Year 1 TomHsiung's Avatar
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    Jan 2013
    Chengdu, Sichuan, China

    Default Some Important Concepts about Clinical Trials

    There are three advantages of the randomized design over other methods for selecting controls.

    First, randomization removes the potential of bias in the allocation of participants to the intervention group or to the control group. Such selection bias could easily occur, and cannot be necessarily prevented, in the non-random iced concurrent or historical control study because the investigator or the participant may influence the choice of intervention. This influence can be conscious or subconscious and can be due to numerous factors, including the prognosis of the participant. The direction of the allocation bias may go either way and can easily invalidate the comparison. This advantage of randomization assumes that the procedure is performed in a valid manner and that the assignment cannot be predicted.

    Second, somewhat related to the first, is that randomization tends to produce comparable groups; that is, measured as well as unknown or unmeasured prognostic factors and other characteristics of the participants at the time of randomization will be, on the average, evenly balanced between the intervention and control groups. This does not mean that in any single experiment all such characteristics, sometimes called baseline variables or covariates, will be perfectly balanced between the two groups. Of course, many covariates are strongly associated; thus, any imbalance in one would tend to produce imbalances in the others. Stratified randomization and stratified analysis are methods commonly used to guard against and adjust for imbalanced randomizations.

    Third, the validity of statistical tests of significance is guaranteed. As has been stated, "although groups compared are never perfectly balanced for important covariates in any single experiment, the process of randomization makes it possible to ascribe a probability distribution to the difference in outcome between treatment groups receiving equally effective treatments and thus to assign significance levels to observed differences." The validity of the statistical tests of significance is not dependent on the balance of the prognostic factors between the randomized groups. The chi-square test for two-by-two tables and Student's t-test for comparing two means can be justified on the basis of randomization alone without making further assumptions concerning the distribution of baseline variables. If randomization is not used, further assumptions concerning the comparability of the groups and the appropriateness of the statistical models must be made before the comparisons will be valid. Establishing the validity of these assumptions may be difficult.
    Last edited by TomHsiung; Sat 7th October '17 at 4:19pm.
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

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