What are two possible sources of bias in this cohort study

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Assignment:

A causal relationship between cigarette smoking and lung cancer was first suspected in the 1920s on the basis of clinical observations. To test this apparent association, numerous epidemiologic studies were undertaken between 1930 and 1960. Two studies were conducted by Richard Doll and Sir Austin Bradford Hill in Great Britain. The first was a case-control study begun in 1947 comparing the smoking habits of lung cancer patients with the smoking habits of other patients.

The second was a cohort study begun in 1951 recording causes of death among British physicians in relation to smoking habits. Data for the cohort study were obtained from the population of physicians listed in the British Medical Register who resided in England and Wales as of October 1951. Questionnaires were mailed in October 1951 to 59.600 physicians. Usable responses to the questionnaire were received from 40,637 physicians, of whom 34,445 were males and 6,192 were females. Because this proportion of male to female physicians was typical of the time, these numbers accurately represented the gender composition of the physician population.

The physicians were asked to classify themselves into one of three categories: 1) current smoker, 2) ex-smoker, or 3) nonsmoker. Smokers and ex-smokers were asked the amount they smoked, their method of smoking, the age they started to smoke, and if they had stopped smoking, how long it had been since they last smoked. Nonsmokers were defined as persons who had never consistently smoked as much as one cigarette a day for as long a year. Information about lung cancer came from death certificates and other mortality data recorded during ensuing years

Based on the information provided here, what are two possible sources of bias in this cohort study?

Explain in detail what these types of bias are, and how they could have occurred in this study. (Do not simply repeat information from notes or textbook).

Based on the information provided here, what are the two possible strengths of this cohort study? Name them and then explain the strength.

Reference no: EM133317349

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