Epidemiology & Biostatistics Cohort Studies

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Chapter objectives

By the end of this chapter, the student should be able to:

  • Recognize and differentiate between key terms.
  • Apply various types of sampling methods to data collection.
  • Create and interpret frequency tables.

You are probably asking yourself the question, "When and where will I use statistics?" If you read any newspaper, watch television, or use the Internet, you will see statistical information. There are statistics about crime, sports, education, politics, and real estate. Typically, when you read a newspaper article or watch a television news program, you are given sample information. With this information, you may make a decision about the correctness of a statement, claim, or "fact." Statistical methods can help you make the "best educated guess."

Since you will undoubtedly be given statistical information at some point in your life, you need to know some techniques for analyzing the information thoughtfully. Think about buying a house or managing a budget. Think about your chosen profession. The fields of economics, business, psychology, education, biology, law, computer science, police science, and early childhood development require at least one course in statistics.

Included in this chapter are the basic ideas and words of probability and statistics. You will soon understand that statistics and probability work together. You will also learn how data are gathered and what "good" data can be distinguished from "bad."

Lect 3: Epidemiology & Biostatistics Cohort Studies

We will teach you how to read and critique medical journal articles using examples from some of the most widely-read medical journals. To critique the medical literature you will need to understand the fundamentals of epidemiologic study design, the sources of bias, and the role of chance. Every discipline has its own jargon. we will cover the terminology used in clinical research, including the basic statistical jargon. The most important concepts are in the lectures and small groups provide you with an opportunity to apply what you have learned from the lecture material to actual medical journal articles.

As future physicians you have an obligation to remain current in your field of practice and to treat patients according to generally accepted standards of care.

Quiz PDF eBook: 
Epidemiology & Biostatistics Cohort Studies
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8 Pages
2014
English US
Educational Materials



Sample Questions from the Epidemiology & Biostatistics Cohort Studies Quiz

Question: Low serum levels of cholesterol have been associated with depression. (This is true! I did not make this up. It is not clear why, but I like to think that ice cream deprivation may be an explanation ?- :) - JEF) Based on this observation, investigators conducted a study to examine the association of serum cholesterol levels and suicide. They used a database from a health maintenance organization to identify persons who had normal cholesterol and persons who had high cholesterol levels identified by their physician at least 10 years ago. The investigators then linked this information to the National Death Index to identify persons who had later died by suicide. What type of study was this?

Choices:

This was a retrospective cohort study. It is a cohort study because the groups were assembled based on their exposure status. It is retrospective because the suicides had already occurred when the investigators began their study. (By the way, they did find an association between low cholesterol and suicide. Perhaps we need to start thinking of ice cream as medicine. :)

Question: To study the question of whether unemployment leads to a higher risk of cardiovascular disease, which study design would be better - a randomized controlled trial or a cohort study? What is your reasoning?

Choices:

It would not be feasible or ethical to randomize volunteers to a state of unemployment. Therefore, the only feasible/ethical study design would be a cohort study.

Question: The following information is for Questions 4?-5 The 1 year risk (i.e. annual incidence) of lung cancer in smokers is 140 per 100,000. The 1 year risk of lung cancer in non?-smokers of the general population is 10 per 100,000.

Choices:

RR=140/100,000 divided by 10/100,000 = 14 Note: When the disease is rare (as is lung cancer) the OR approximates the RR.

Question: Cohort studies do not involve randomization. What advantage does randomization confer to a randomized controlled trial that does not exist in cohort studies?

Choices:

We learned in the session on randomized controlled trials that one of the important advantages of randomization is that it results in two groups that have comparable risk profiles - especially if the trial is a large one. Since cohort studies do not involve randomization, the exposed and unexposed groups may have very different risk profiles. This creates a problem called confounding which we will discuss in more detail in a later session.

Question: The following information is for Questions 6?-7 The 1 year risk (i.e. annual incidence) of lung cancer in smokers is 140 per 100,000. The 1 year risk of lung cancer in non?-smokers of the general population is 10 per 100,000. Smoking in bars was banned, in part, because of epidemiologic evidence of ill?-effects of second hand smoke on food service workers. non?-smoking food service workers have a 50% higher risk of lung cancer than non?-smokers of the general population.

Choices:

The attributable risk is the risk difference calculated as 15/100,000 - 10/ 10,000 = 5 per 100,000 at risk per year. In this example, you should think of the rate of lung cancer in non?-smokers of the general population as being the ?gbackground rate?h or lung cancer due to other causes, such a radon exposure. Interpretation of the attributable risk: Five cases of lung cancer per 100,000 food service workers exposed to second hand smoke could be avoided by banning smoking in bars and restaurants.

Question: The following information is for Questions 6?-7 The 1 year risk (i.e. annual incidence) of lung cancer in smokers is 140 per 100,000. The 1 year risk of lung cancer in non?-smokers of the general population is 10 per 100,000. Smoking in bars was banned, in part, because of epidemiologic evidence of ill?-effects of second hand smoke on food service workers. non?-smoking food service workers have a 50% higher risk of lung cancer than non?-smokers of the general population.

Choices:

If the incidence rate of lung cancer in non?-smokers is 10 per 100,000 at risk per year, and food service workers have a 50% higher rate than this, then food service workers have an annual rate of lung cancer of 15 per 100,000 at risk.

Question: Consider the following article. Meat Intake and Mortality A Prospective Study of Over Half a Million People Sinha et al. Arch Intern Med. 2009;169(6):562?-571 Background: High intakes of red or processed meat may increase the risk of mortality. Our objective was to determine the relations of red, white, and processed meat intakes to risk for total and causespecific mortality. Methods: The study population included the National Institutes of Health.AARP (formerly known as the American Association of Retired Persons) Diet and Health Study cohort of half a million people aged 50 to 71 years at baseline. Meat intake was estimated from a food frequency questionnaire administered at baseline. Conclusion: Red and processed meat intakes were associated with modest increases in total mortality, cancer mortality, and cardiovascular disease mortality. What study design was most likely used? Explain your reasoning.

Choices:

The study was most likely a prospective cohort study. The title states the study was prospective. Meat consumption was measured as it occurred naturally in the study volunteers. No intervention was mentioned.

Question: The following information is for Questions 4?-5 The 1 year risk (i.e. annual incidence) of lung cancer in smokers is 140 per 100,000. The 1 year risk of lung cancer in non?-smokers of the general population is 10 per 100,000.

Choices:

Putting the numbers in a 2x2 table format is easiest to calculate an OR A=140 B=99,860 OR=AD/BC or 140*99,990 / 10*99,860 = 14 C=10 D=99,990 Interpretation: over 1 year, smokers are 14 times as likely to develop lung cancer as non?-smokers Note: The OR is interpreted in exactly the same way as a RR.

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Source:  Janet, E.A. Forrester, Kwan Ho Kenneth Chui, Steven Cohen, Michael D. Kneeland, Alice Tang, David Tybor. Epidemiology and Biostatistics 2010. (Tufts University OpenCourseWare), http://ocw.tufts.edu/Course/65/ (Accessed 3 May, 2014). License: Creative Commons BY-NC-SA
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