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

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

Threshold	Risk that the attained power falls below the threshold value
Threshold	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%

^aResults are for unrestricted randomization in Example 1.
^bResults are for unrestricted randomization in Example 4.
^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.

ISSN: 1745-6215