Chapter 6.2, Problem 7E

The article “The Effect of Restricting Opening Hours on Alcohol-Related Violence” (S. Duailibi, W. Ponicki, et al., American Journal of Public Health, 2007:2276–2280) presented homicide rates for the years 1995–2005 for the town of Diadema, Brazil. In 2002, a law was passed requiring bars to close at 11 pm each night. After the law’s passage, the homicide rate dropped by an average of 9 homicides per month, a statistically significant decrease. Which of the following is the best conclusion?

1. i. It is reasonable to conclude that the law is responsible for a reduction of 9 homicides per month.
2. ii. It is reasonable to conclude that the law is responsible for a reduction in homicides, but the actual amount might be somewhat more or less than 9 per month.
3. iii. It is reasonable to conclude that the homicide rate decreased, but the law may not have anything to do with the decrease.
4. iv. It is plausible that the homicide rate may not have decreased at all after the passage of the law.