Read the excerpt from the following abstract from a controlled experiment, and then:
a. Identify the treatment and response variables.
b. Restate the conclusion of the study in terms of a cause-and-effect conclusion.
"We randomly assigned adults undergoing clean-contaminated surgery in six hospitals to preoperative skin preparation with either chlorhexidine-alcohol scrub or povidone-iodine scrub and paint. The primary outcome was any surgical-site infection within 30 days after surgery. Secondary outcomes included individual types of surgical-site infections. The overall rate of surgical-site infection was significantly lower in the chlorhexidine-alcohol group than in the povidone-iodine group (9.5% vs. 16.1%; P = 0.004; relative risk, 0.59; 95% confidence interval, 0.41 to 0.85). Chlorhexidine-alcohol was significantly more protective than povidone-iodine against both superficial incisional infections (4.2% vs. 8.6%, P = 0.008) and deep incisional infections (1% vs. 3%, P = 0.05) but not against organ-space infections (4.4% vs. 4.5%).
Conclusions: Preoperative cleansing of the patient's skin with chlorhexidine-alcohol is superior to cleansing with povidone-iodine for preventing surgical-site infection after clean-contaminated surgery."