The city of Ottawa, Canada, passed a law banning smoking in bars and restaurants. Along with the bar and restaurant owners, a group of researchers wanted to know if the smoking ban would hurt sales figures (Luk, Ferrence, & Gmel, 2006). They kept track of bar and restaurant sales every month, starting two years before the smoking ban and continuing for ten months after the smoking ban. They noticed that although sales fluctuated greatly from month to month, there was no overall change in the sales trend after the smoking ban started. Answer one or more of the following questions: 

a. Determine whether the study is a nonequivalent control group design, an interrupted time-series design, or a nonequivalent groups interrupted time-series design.

b. What causal statement is the researcher trying to make, if any? Is it appropriate? If the researcher is making a causal statement, use the results and design to interrogate the study's internal validity. If you notice an internal validity flaw, can you redesign the study to remove the flaw?

c. If the researcher has a null effect, ask questions to interrogate the null effect.

d. Ask one question to address construct validity and one to address external validity.