A study published in 2010 in The New England Journal of Medicine investigated the effect of financial incentives on smoking cessation. As part of the study, 878 employees of a company, all of whom were smokers, were randomly assigned to one of two treatment groups. One group (442 employees) was to receive information about smoking cessation programs, while the other (436 employees) was to receive that same information, as well as a financial incentive to quit smoking. The primary endpoint of the study was smoking cessation status six months after the initial cessation was reported. After implementation of the program, 14.7% of individuals in the financial incentive group reported cessation six months after the initial report, compared to 5.0% of the information-only group.
a. For this study, identify the experimental units, explanatory and response variable(s), and treatments.
b. Assuming the observed difference in cessation rates between the groups (14.7, - 5.0, = 9.7, ) is statistically significant, is this convincing evidence that the difference was due to the effect of the financial incentive and not due to ordinary random variation?