Non-randomised studies

In March 2008, a regulation was introduced in New York City that required restaurants to provide calorie information on all food purchases. The regulation applied only to restaurants with 15 or more stores nationwide. Researchers assessed the effects of the regulation on individual purchases. The primary outcome was the energy content of individual purchases, based on customers’ register receipts and the information provided on menus within the restaurant.1

A random sample of 168 locations of the most popular fast food chains in New York City was obtained. For nine weeks in the spring of 2007 and then again in the spring of 2009, all adult lunchtime customers at the sampled locations were interviewed. In total, 7309 adult customers were interviewed in 2007 and 8489 in 2009. The mean number of calories purchased after the regulation was slightly higher than that before, although the difference was not statistically significant (846 v 828; P=0.22).

Which one of the following best describes the above study design?

• a) Non-randomised controlled trial

• b) Cohort …