A random-digit dialed survey conducted in the city of long beach, california reported that a greater proportion of nonsmokers endorsed a ban on smoking in alcohol-serving establishments than did smokers. What type of study design was this?

The correct answer is case-control study.

Explanation:

In a case-control study, two groups of the population are used, in which one group is kept as control, and the other is known as the experimental group that encounters with a specific disease or an outcome. With the help of this study, one can expose the groups to various or single outcomes.  

In the given case, a study is done in which an advertisement on a ban on smoking is encouraged by the non-smokers at the alcohol sale points but not by smokers, in the process a random digit dialing method was used. This random digit dialing method is an illustration of a case-control study, in which the survey of the individuals is done regarding the ban on smoking.