A researcher from a state health department obtained routinely-collected data from 2015 on the prevalence of chronic obstructive pulmonary disease (COPD) by each county in the state.

A researcher from a state health department obtained routinely-collected data from 2015 on the prevalence of chronic obstructive pulmonary disease (COPD) by each county in the state. They also collected information on the number of days exceeding 90 degrees F per county during 2015. After completing statistical analyses, she concludes that counties with more hot days also had higher rates of COPD. a. (1 point} What type of study design was used? i. Case report/case series ii. Cross-sectional study using ecologic data (ecologic study) iii. Cross-sectional study iv. Case-control study v. Prospective cohort study vi. Retrospective cohort study vii. Randomized trial b. (2 points) Justify your answer from part a.