A study was conducted concerning the effectiveness of an aspiration risk-reducing program. The incidence of aspiration was compared between the usual care group (n=32) and the Aspiration Risk-Reduction protocol (ARP) (n=145). One aspect of the protocol involved higher elevation of the head of the bed for patients in the ARP group. Aspiration was significantly lower in the ARP group patients than the usual care group patients, as determined by a lower mean percentage of pepsin-positive tracheal secretions (p=0.001). The incidence of at least one aspiration was half as likely in the ARP group as in the usual care group.

What statistical test was used?

Group of answer choices

a. Pearson r

b. Spearman's rho

c. t-test

d. chi-square