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Allocation Concealment


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Allocation Concealment

  2. 2. DEFINITION  Allocation concealment refers to preventing the next assignment in the clinical trial from being known.  Allocation concealment refers to the technique used to implement the sequence, not to generate it.
  3. 3.  Allocation concealment has nothing directly to do with randomization.  It has nothing to do with blinding doctors or patients while getting or giving therapy.  It makes sure that patients enroll into a study without knowing which arm of the study they will be assigned to and preventing the providers or researchers on site from interfering with the randomized allocation process.
  4. 4. EXAMPLE 1:  If the referring health care provider knows the next subject will be allocated to Slimmenow, he/she may be inclined to try to help a certain patient he/she thinks may benefit more.  This will introduce selection bias that the randomization was designed to eliminate.
  5. 5. EXAMPLE 2:  Subjects are probably hoping to be randomized to Slimmenow. If a subject becomes aware of the allocation scheme prior to enrollment, knowledge of allocation to placebo might cause the subject to refuse to participate entirely.  Or, the subject may wait until the allocation is to the active drug before enrolling.  Again, the results are loss of randomization and introduction of bias.
  6. 6. IMPORTANCE OF ALLOCATION CONCEALMENT Trials that used inadequate or unclear allocation concealment: 1. Yield up to 40% larger estimates of effect. 2. Yield greater heterogeneity in results. 3. Allows bias to seep into trials.
  7. 7.  Moreover, the results of such a trial can be more damaging than similar results from an explicitly observational research study.  Biases are usually assumed and acknowledged in observational studies, and the statistical analysis and eventual interpretation attempt to take those biases into account.  Conversely, studies labeled as randomized are frequently assumed to be free of bias.
  8. 8.  Consequently, the credibility of randomized controlled trials lends support to faster and greater changes in clinical or preventive management.  If it is based on a compromised study, squanders scarce health resources, or even worse, harms peoples’ health.
  9. 9. DECIPHERING REASONS:  Researchers might want certain patients to benefit from one of the treatments, or the trial results to confirm their beliefs.  An absence of knowledge of the scientific ramifications of such actions.  the deciphering of the allocation scheme might frequently become too great an intellectual challenge to resist
  10. 10. EXAMPLES OF METHODS OF DECIPHERING ALLOCATION CONCEALMENT 1. Holding translucent envelopes up to bright lights to reveal upcoming assignment. 2. Opening unsealed assignment envelopes. 3. Opening a well-sealed, opaque envelope in advance of consent. 4. Opening unnumbered envelopes until desired allocation found. 5. Determining different weights of the assignment envelopes. 6. Asking a central randomization center for the next several assignments all at once. 7. Deciphering assignments to active drug or placebo based on appearance of drug container labels.
  11. 11. SUGGESTED MINIMUM AND EXPANDED DESCRIPTIONS OF ALLOCATION CONCEALMENT 1. Sequentially numbered, opaque, sealed envelopes (“SNOSE”). 2. Sequentially numbered containers. 3. Pharmacy controlled. 4. Central randomization.
  12. 12. 1. SEQUENTIALLY NUMBERED, OPAQUE, SEALED ENVELOPES (“SNOSE”)  Description of details on how tampering and discovery was prevented (eg, carbon paper lined to create an audit trail, aluminum foil or cardboard placed inside to prevent “hot lighting”)
  13. 13. 2. SEQUENTIALLY NUMBERED CONTAINERS  Description provides details of no detectable differences between containers. Containers were equal in weight, similar in appearance, and tamper-proof.
  14. 14. 3. PHARMACY CONTROLLED  Description provides indications that the researchers developed or validated a proper randomization scheme for use by the pharmacy. Description that the pharmacy was provided instruction in allocation concealment.
  15. 15. 4. CENTRAL RANDOMIZATION  Mechanism for contact is described (eg, telephone, e-mail, fax). Precautions taken to ensure enrollment prior to allocation as well as description of training for individuals staffing the central office are provided.
  16. 16. CONCLUSION  Proper randomisation remains the only way to avoid selection and confounding biases.  Randomised controlled trials antagonise human beings by frustrating their clinical inclinations. Thus, many involved with trials will be tempted to undermine randomisation, if afforded the opportunity to decipher assignments.  To minimise the effect of this human tendency, trialists must devote meticulous attention to concealment of allocation schemes, because proper randomisation hinges on adequate allocation concealment.
  17. 17. THANK YOU