Alas, we got an error message similar to the one from Subsection 8.5.1: infer is telling us that one of the levels of the categorical variable yawn needs to be defined as the success. Recall that we define success to be the event of interest we are trying to count and compute proportions of. Are we interested in those participants who "yes" yawned or those who "no" didn’t yawn? This isn’t clear to R or someone just picking up the code and results for the first time, so we need to set the success argument to "yes" as follows to improve the transparency of the code: