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Table 1 The risk that the attained power will fall below selected threshold values

From: The randomization-induced risk of a trial failing to attain its target power: assessment and mitigation

Threshold Risk that the attained power falls below the threshold value
Example 1 (unrestricted)a Example 4 (unrestricted)b Example 4 (restricted)c
72% 0.6% 0.0% 0.0%
73% 1.7% 0.2% 0.0%
74% 1.7% 1.0% 0.0%
75% 3.8% 2.7% 0.0%
76% 3.8% 7.3% 0.0%
77% 8.1% 16.6% 0.0%
78% 15.4% 33.5% 0.0%
79% 26.8% 57.9% 0.0%
80% 87.5% 81.0% 5.4%
81% 100.0% 97.8% 68.0%
82% 100.0% 100.0% 99.0%
83% 100.0% 100.0% 100.0%
  1. aResults are for unrestricted randomization in Example 1.
  2. bResults are for unrestricted randomization in Example 4.
  3. cResults are for a randomization algorithm that allows only allocations with the four largest clusters transitioning at the first or last steps (two clusters at each of these steps) in Example 4.