Using the key below, classify each of the following descriptions of epidemiologicalstudies according to study type. In your answer nominate if the study type is

descriptive, analytical or experimental and also provide two (2) reasons for your choice of study type

(for example, if you believe a particular description relates to a Cross-Sectional study nominate if it is an example of a descriptive, analytical or experimental study type AND provide two (2)reasons why you believe it is a Cross-Sectional study).

KEY (Study Type)

A Descriptive study
B Ecological study
C Cross-Sectional study
D Case-Control study
E Retrospective Cohort study
F Prospective Cohort study
G Randomised Controlled Trial
H Community Trial

a) A total of 825 insulation workers employed between 1941 and 1944 was identified from the personnel records of three large insulation manufacturing plants in the south-eastern United States in 1975. During the period 1941-1975, 26 deaths from lung cancer were discovered among the workers. Only six lungcancer deaths, however, were reported among a comparable group of 700 coworkers who did not work with insulation during the same time period. The investigators had postulated that exposure to the insulation material increases the risk of lung cancer.

b ) To see if hypnosis could reduce chronic pain, investigators randomly assigned 120 volunteers with osteoarthritis to either hypnosis therapy or a control group. Pain levels were checked among the subjects every three months during the 12- month study using validated pain measures. Those assigned to the hypnosis group reported reduced pain compared to those in the control group after three and six months, but not after nine and 12 months, of follow-up.

c) To find out if planting grass on the top of buildings would be effective in reducing air pollution levels in polluted cities, investigators selected two adjacent cities with similar demographic profiles and air pollution levels. The officials of one city agreed to plant grass on all its public buildings in the downtown area and on all private buildings where consent could be obtained. The other city did not plant any grass on the top of its buildings. After two years of follow-up, the city that planted grass on the buildings had lower air pollution levels than the city that did not plant any grass, although the difference was not significantly different.

d) A study was undertaken to test the hypothesis that chewing tobacco increases the risk of stomach cancer. Detailed historical data on chewing tobacco use were collected from 400 subjects with newly diagnosed stomach cancer and 400 subjects without stomach cancer. The results revealed that chewing tobacco was not a significant risk factor for stomach cancer.