The district attorney's office wants further evidence of the results found in the bystanders and thieves study. It decides to conduct a study using data from reported thefts over the past five-year period. Police records indicate whether bystanders who report a crime are alone when the crime is observed or are accompanied by one or more people. The district attorney's office will assess whether more theft reports indicate that the witness was alone or with other people.Which type of study is being conducted by the district attorney's office?