Stats Task 4: Cohort Studies and Interpreting Relative Risk

You have been asked to respond to Andy, who has questions about why his team chose the Cohort Study for their investigation of lung cancer in Uintah. In addition, he needs help in determining what the Relative Risks (RR) tell him about how exposure to the gases from a volcano eruption are related to developing lung cancer.

The following step-by-step guide will help you do your work.

1. Before you begin your work, find a peer to work with for this task. Although each of you will be responsible for submitting your own work, you may work with one another to better analyze the question and come up with the important components of your response. You may partner with someone you have worked with before, with more than one person, or as otherwise advised by your mentor.
   
   
2. Review the email and make sure you understand what questions you are being asked to answer in this task. It may be helpful to print a copy of the email as it also contains the results of the investigation which you will need to answer questions about what the results mean.
   
   
3. Review the Resources available for this task, specifically the FAQs, which will help you to consider the important characteristics and differences between the case-control and cohort studies. You will refer back to these FAQs throughout this task.

Compare and Contrast a Case-Control and Cohort Study

Each study is designed for different purposes and gives the researcher different results. Determining which study to conduct is an important step in epidemiology. This mini-task will give you some experience with the different studies so you can better answer Andy’s questions.

Tip: If you have any difficulty during this mini-task, go back to the Resources section first. If you still have questions, check-in with your mentor.

1. In the Resources section (above), take another look at the Case-Control and Cohort Study FAQ. The FAQ provides an overview of the two types of studies and describes what the calculations in each study mean. It may be helpful to refer back to this file periodically as you complete the other parts of this task.
   
   
2. In the Resources section, take another look at the Synopsis of Doll and Hill’s Classic Case-Control and Cohort Studies about two important studies about smoking and lung cancer. Review the questions/answers from the previous task with a special emphasis on cohort studies this time.

Uintah Lung Cancer

1. Now think about the lung cancer investigation that Andy summarizes in his email. With your partner, answer the following questions:
   
   1. In this study, what did the team know at first? Did they know there was an outcome (outbreak or illness) or an exposure?
      
      
   2. In their investigation, what are they trying to find out?
      
      Tip: Think in terms of exposures and outcomes.
      
      
   3. Why didn’t the team choose to do a case-control study in Uintah?
      
      
   4. How would the two comparison groups be defined in this study?
      
      
   5. What does the RR tell you about the relationship between exposure to volcanic gases and lung cancer?
      
      
      • What implications do these RR have from a public health standpoint?
        
        
   6. How does the RR in the women cohort compare with the RR in the men cohort?
      
      • What are some possible reasons why there are differences between the two groups?
        
        TRAP! Don't forget to consider Type I and II errors, biases, and confounding factors.
        
        
      • Is more information be needed to establish why there are differences between the genders? If so, what might Andy and his team need to do in order to investigate the situation further?
        

Draft the Email Response

1. This time, without your peer, draft an email response answering Andy’s questions about his team’s study.
   
   
• Tell Andy why you think his team chose the cohort study over the case-control study for their investigation in Uintah. Make sure to identify which factors are important to consider when deciding between doing a cohort Study and a case-control study so that he will be able to answer similar questions that may arise in the future without assistance. (Note: This response should focus more on the factors for cohort studies with some information on case-control studies for clarification as needed.)
  
  
• Tell Andy what the results of the Uintah cohort study tell him about relationship between exposure to volcano gases and lung cancer. Make sure to tell him how to interpret relative risks in general so he'll be able to answer similar question in the future without assistance.
  
  
• Look at Andy's email for questions involving cohort studies and risk ratios and how they're related to other things you've learned about epidemiology investigations. Answering the less ovbious questions in his email can help him tie the information you've given him to what he already knows about epi investigations.
  
  
• Make your email response clear and concise. It should be easy to understand and not include any information that would be distracting to the reader. Include examples as needed while still keeping the email on point.
  
  
2. Next, conduct a review of your email responses by exchanging responses with your peer.
   

• Review one another’s email response to determine if the email meets the requirements listed above. If an email response does not meet all of the requirements, help one another identify how it can be modified to be more clear and/or complete.
  
  
• While it is appropriate to work together on this task, make each of your responses unique, including unique examples as appropriate, to reflect your own work and thinking.

3. Submit your individual response to your mentor. Review the checklist located in the Submit Your Work section of this task before submitting your response to your mentor.

Stats Task 4 Resources

The resources below will help you get started on this task. You may decide to do additional research to help clarify concepts, or to gain a deeper understanding of the subject matter. View the General Skills Resources link on the left for more information on research including evaluating web resources.

While Wikipedia is a valuable resource, unlike some other websites anyone can contribute to or modify the site (whether they're knowledgeable about the topic or not). As a result, the site is subject to constant change by questionable sources. Be sure to cross-check information on Wikipedia with other reputable sites to ensure accuracy.

Hypotheses and the Scientific Method FAQ
This FAQ supports you in creating and testing scientific hypotheses, with examples and explanations.

Hypotheses for Epidemiology FAQ
General information on hypotheses and testing with emphasis on hypotheses for epidemiology studies.

Synopsis of Doll and Hill’s Studies
A description of Doll and Hill's classic case-control and cohort study on the relationship between smoking and lung cancer. Includes a comparison of the two types of studies.

Case-Control and Cohort Study FAQ
Frequently Asked Questions about Case-Control and Cohort studies including the steps involved in each study, the advantages and disadvantages to each, how to calculate Odd Ratios and Relative Risk, and how to interpret the results.

Case-Control Studies and Refining Hypotheses
Information on case-control studies, selecting controls, and refining hypotheses. The first two pages and the last two pages are the most informative for this task.

Case-Control and Cohort Diagram
A visual diagram of the two types of studies, including participant selection and the relation of exposures and outcomes in each group.