I have an experiment with several treatments and one control group. There are three scenarios in the experiment, and every scenario has several treatments. I have constructed the survey so that every scenario corresponds to one block, and the treatments are then administered as randomly assigned question (with only descriptive text) within the blocks. This works well, except for the fact that I want to make sure that individuals who are assigned to the control group only get the control in all three scenarios. My initial solution to this problem was to create a control block, in addition to the three scenario blocks where treatments are administered. However, since Qualtrics randomizes with even probabilities across blocks, this would lead to 1/4 of the participants being assigned the control scenario. Ideally, I would like to assign 1/10 of the respondents to the control group, since my most interesting comparisons for this experiment is across different treatment groups. The control
I'm setting up a survey where I need to use Qualtrics's random number generator to assign respondents to different scenarios. I've tried to find information about how the random number generator works, but have found little documentation. I'm assuming that all numbers are drawn from a discrete uniform distribution, but am I wondering if anybody has more information on this or has actually tested this. As a rough test, I sampled approximately 220 random numbers from the generator and got the following results (apologies for the huge images, I could not figure out how to make them smaller): !
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