Timeline for When using stratified randomization in a RCT, how many envelopes per stratum should be prepared?
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| Sep 12, 2011 at 15:16 | comment | added | whuber♦ | @propofol I don't understand the role of "historical probabilities" here. My understanding is that the experiment is under your control and that you are randomizing using a random number generator; therefore, the probabilities are determined, not estimated. Perhaps you could edit your question to elaborate on exactly how randomization is being used in this experiment. | |
| Sep 11, 2011 at 23:34 | comment | added | pmgjones | Thank you. Useful answer. For experienced trialists, though, I still wonder what the "rule of thumb" is for stratified RCTs whose historical probabilities are not as firmly known. What if I could only say "I expect 40-60% to be open, 20-40% closed, and the rest combined"? Any disadvantages of creating more envelopes than necessary, as long as blocked randomization is used? | |
| Sep 11, 2011 at 22:37 | history | answered | whuber♦ | CC BY-SA 3.0 |