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Allocation Concealment
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Allocation Concealment






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Allocation Concealment Allocation Concealment Presentation Transcript

  • 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.
  •  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. View slide
  • 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. View slide
  • 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.
  • 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.
  •  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.
  •  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.
  • 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
  • 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.
  • 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.
  • 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”)
  • 2. SEQUENTIALLY NUMBERED CONTAINERS  Description provides details of no detectable differences between containers. Containers were equal in weight, similar in appearance, and tamper-proof.
  • 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.
  • 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.
  • 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.