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; the other (436 employees) was to receive that same information as well as a financial incentive to quit smoking. The outcome of interest 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. Assume that the observed difference in cessation rates between the groups 114.7% - 5.0% = 9.7%2 is statistically significant.
a. What does it mean to be statistically significant? (choose the best option from (i)–(iv))
i. The financial option was offered to 9.7% more smokers in the study than the nonsmokers who were employees of the company.
ii. 9.7% was calculated using statistical techniques.
iii. If there were no true impact of the financial incentive, the observed difference of 9.7% is unlikely to have occurred by chance alone.
iv. We know that if the financial incentive were given to all smokers, 9.7% would quit smoking.
b. Is the difference between the groups attributable to the financial incentive?