In a study of treatments for very painful "cluster" headaches, 156 patients were treated with oxygen and 145 other patients were given a placebo consisting of ordinary air. Among the 156 patients in...

identify the test statistic

Extracted text: In a study of treatments for very painful "cluster" headaches, 156 patients were treated with oxygen and 145 other patients were given a placebo consisting of ordinary air. Among the 156 patients in the oxygen treatment group, 115 were free from headaches 15 minutes after treatment. Among the 145 patients given the placebo, 22 were free from headaches 15 minutes after treatment. Use a 0.05 significance level to test the claim that the oxygen treatment is effective. Complete parts (a) through (c) below. P2 Identify the test statistic. (Round to two decimal places as needed.)