A company that owned several hospitals in rural areas of the south went bankrupt and, over a couple of months, closed the hospitals it operated. Researchers became aware of this situation and used public health records to document average age at death of residents in those communities where the hospitals closed and in communities that were matched on several variables but did not lose their hospitals. The researchers collected death records for several years before and after the closure of these hospitals to look at the effect the closure had on life expectancy. Which type of research design are the researchers using