Question

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.

Answer 1

Answers are written in BOLD in the explanation below.

Explanation:

(A) The study was done in 1975 but the 825 insulation workers were employed or worked between 1941 and 1944. This makes the study a RETROSPECTIVE study.

There is an exposed group (insulation workers) and an unexposed group (coworkers who did not work with insulation). In addition (an additional reason), the study begins with exposed patients and then unexposed patients. These reasons make it a COHORT study.

This study is also an ANALYTICAL study, as the investigators made a postulation, based on analysis of the number of lung cancer deaths among non-insulation workers and the number of lung cancer deaths among insulation workers.

This is also an ECOLOGICAL study, as study results are applicable only at population level.

(B) This is an EXPERIMENTAL study, as the researcher/investigator seeks new knowledge by selecting groups to derive certain data from; in a step by step manner.

Due to the random selection of subjects (volunteers) and random assignment of them to the two groups, this is a RANDOMIZED TRIAL.

The presence of similar experimental and control groups (all volunteers/subjects have osteoarthritis) is a key feature of RANDOMIZED CONTROLLED TRIAL.

After the selection of subjects, experiment of pain levels was conducted for some months (up to a year). This makes the study a PROSPECTIVE study because there was follow-up on the groups, to see who develops the outcome of interest.

The fact that there was no experimental report after 9 and 12 months of follow-up is another key feature of the RCT because in a RCT, the investigator often faces issues like dropout and noncompliance of subjects.

(C) This is a COMMUNITY TRIAL study because two cities/communities are experimented on.

This is also an EXPERIMENTAL study. The fact that both cities have similar demographic profiles and air pollution levels confirms a key feature of experimental studies. There is a 2-year follow-up. This is another reason why the study is experimental and PROSPECTIVE.

(D) This is an OBSERVATIONAL study. This is because already available data was collected and simply looked upon or observed, to know if chewing tobacco was a significant risk factor for stomach cancer.

The data is historical data, hence this is a RETROSPECTIVE study.

This is also a CROSS-SECTIONAL study because it is observational in nature and it gives characteristics of subjects at a single point in time, not over a period of time. It does not have a follow-up period and cannot provide cause-effect relationship between variables.

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