**Medical errors are common in hospitals throughout the world. One possible causal factor is the long work hours hospital personnel. In a pilot study investigating the issue, medical residents were encouraged to sleep 6-8 hours per night for a 3-week period instead of their usual irregular sleep schedule. The researchers expected, given previous data, that there would be one medical error per resident per day on the usual irregular sleep schedule.

Suppose two residents participate in the program (each for 3 weeks), and chart review finds a total of 20 medical errors made by two residents combined.

What test can be used to test the hypothesis that an increase in amount of sleep will change the number of medical errors per day?