A researcher wanted to check whether marriage causes people to become more


responsible. Specifically, he was interested to know if marriage causes people to


become more careful drivers.


He went over the files of all car accidents that occurred in the past 3 years in his


state, and he calculated how many accidents out of the total number of accidents


were caused by married people. Then, he compared his results with the actual


percentage of married people in his state.


What type of statistical study did the researcher use?