In this study, researchers investigated associations between environmental radon concentration and the incidence of various types of skin cancer. They analyzed data for 287 small areas (postcode sectors) in southwest England for the years 2000-2004. England's cancer registry was used to generate incidence rates of malignant melanoma, basal cell carcinoma, and squamous cell carcinoma by postcode sector. Analyses were adjusted for potentially confounding factors, including average age, percent male, and percent living below poverty for each zip code.

Based on the above

(1) What is the study design used?

(2) Is the study observational or experimental?

(3) Is the study descriptive or analytic?

(4) Is the study prospective, retrospective, or cross-sectional?