Biglan et al. (1996) studied whether store clerks in eight Oregon towns were willing to sell tobacco products to minors. They measured clerk behavior repeatedly over time, implemented a positive reinforcement intervention at different times in different towns, and usually found a drop in willingness to sell after implementing this intervention. What research methodology did they use? (CSLO 5)
Group of answer choices
multiple baseline design.
interrupted time-series design.
nonequivalent comparison group design.
both "a" and "b"