A researcher notices that residents in memory care seem to fall less at night in private rooms than in semi-private rooms. To assess the validity of this impression, the researcher decides to analyze the average falls for a random sample of 36 memory care residents in private rooms versus a random sample of 36 memory residents in semi-private rooms. The records indicate that 18 residents fell during the study period in private rooms while 27 residents from semi-private rooms fell.

Calculate the test statistic?: