Cause Is this association causal?

Cause Is this association causal?
RR = 7 In Investigation 3-2: Cause, students will learn to appreciate what epidemiologists mean when they say that an exposure and an outcome are associated. They will begin to explore the first of several explanations for finding an association: causation. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Where are we and where are we going?
1 How is this disease distributed? Hypotheses 2 Is there an association? 3 Is the association causal? Why did the exposure and the disease turn up together? What’s my hypothesis? Did the exposure and the disease turn up together? Why did the exposure and the disease turn up together? 4 What should be done to prevent the disease? Remind students again that in the Module 3 investigations, they are learning how to answer the third Essential Question: “Is the association causal?” Next Slide 5 Did the prevention strategy work? Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Is the association causal?
Outcome No Outcome Total b d a c Exposure No Exposure The slide shows headlines from newspapers about things that “turn up together.” Read through the headlines. Ask students to picture the 2 x 2 tables that would have been the basis for each of these headlines. They should then visualize the numbers in each cell of the 2 x 2 tables that would have been the basis for each of these headlines. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Is the association causal?
IS ASSOCIATED WITH IN Explain that this slide shows a cartoon about the headlines. The newscaster in the cartoon is spinning three wheels to decide which news he will report. Ask students: ■ What is the point of the cartoon? (Given the frequency with which we hear about associations on the news, we might assume, incorrectly, that those associations are not based on scientific investigation.) Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Intro to Epidemiology – Investigation 3-2: Cause
Review What do epidemiologists and mean when they say that two things, an exposure a disease, are associated with each other? Ask students: ■ What do epidemiologists mean when they say that two things, an exposure and a disease or other health-related outcome, are associated with each other? ■ If an exposure and an outcome are associated with each other, how will the data from an analytical epidemiologic study be distributed in a 2 x 2 table? Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Review Outcome No Outcome Relative Risk Risks Count Exposure No Exposure or % a b c d or 10% Compare Divide To an epidemiologist, an association between an exposure and an outcome exists when there is a large difference between the risks of the outcome in exposed and unexposed groups of people. They determine this by creating a 2 x 2 table and counting, dividing, and comparing. Epidemiologists count the number of people who have and do not have the exposure, count the number of people who have and do not have the outcome, and place those counts in the four cells of a 2 x 2 table. Next, they divide to calculate the risks of the outcome in the exposed and unexposed groups. Then they compare the risks of the outcome in the exposed and unexposed groups by calculating a relative risk. If the relative risk is large, epidemiologists conclude that the exposure and the outcome turned up together and are associated. Next Slide What do epidemiologists mean when they say two things, an exposure and a disease, are associated with each other? Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Review Count Compare Divide
Risks Relative Risk Outcome No Outcome 100 1 99 Count 100% 100 1 Divide 1% Exposure No Exposure or a b 100 Compare c d or Ask students: ■ In the example shown on the slide, when epidemiologists counted, divided, and compared, did the exposure and outcome turn up together? (Yes) Now ask students: ■ Were the exposure and the outcome associated? (Yes) Next Slide Did the exposure and the outcome turn up together? Were the exposure and the outcome associated? Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Relative Risk Outcome No Outcome Risks 100 30 70 Count 30% 30 100 Divide Exposure No Exposure or a b 1 Compare c d 90 or Ask students: ■ In the example shown on the slide, when epidemiologists counted, divided, and compared, did the exposure and outcome turn up together? (No) Now ask students: ■ Were the exposure and the outcome associated? (No) Next Slide Did the exposure and the outcome turn up together? Were the exposure and the outcome associated? Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Relative Risk Outcome No Outcome Risks 100 10 30 70 90 Count 30% 30 100 10 Divide 10% Exposure No Exposure or a b 3 Compare c d 90 or Ask students: ■ In the example shown on the slide, when epidemiologists counted, divided, and compared, did the exposure and outcome turn up together? (Yes) Now ask students: ■ Were the exposure and the outcome associated? (Yes) Next Slide Did the exposure and the outcome turn up together? Were the exposure and the outcome associated? Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Review 1. Cause 2. 3. 4. In the next five investigations, students will explore five different explanations for why two things turn up together. In Investigation 3-2: Cause, students will explore one reason why an exposure and an outcome occur together: because the exposure causes the outcome. Next Slide 5. Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Review Ask students: ■ What does “cause” mean? Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Review Epi Speak Cause Anything that produces an effect. Ask students to find “Cause” in the Epi Speak list. Review its definition. ☼ Teacher Alert: Students’ concepts of cause and effect may be limited to those that are obvious, immediate, and one to one—for example, being hit by a baseball causes pain. However, this is not the case with all cause-effect relationships. A virus that causes a head cold several days after exposure is not obvious, immediate, or one to one. Address misconceptions. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

2 x 2 Table Identify the cells of the 2 x 2 table in which there would be people if the exposure caused the disease. 1 O No O X No X a a b c d d Give each student an Investigation 3-2: Epi Log Worksheet. Students should complete Part 1 on their Investigation 3-2: Epi Log Worksheets by identifying the cells of the 2 x 2 table in which there would be people if an exposure caused a disease or other health-related outcome. ☼ Teacher Alert: We expect students to first conclude that the people would be in cell a, that is, that people who are exposed would have the outcome. With prompting, they may also identify cell d, that is, that people who are not exposed would not have the outcome. We do not expect students to identify b and c at this point. However, by the end of this investigation, they should appreciate why it is possible to also have some people in cell b (people who are exposed and do not have the outcome) and in cell c (people who are not exposed and have the outcome) and still conclude that it is possible for the exposure to cause the outcome. After students have responded, tell them they will later return to their answers to this question. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Cigarette Labels Point out that one of the four different labels appearing on the sides of cigarette packs reads “SURGEON GENERAL’S WARNING: Smoking Causes Lung Cancer, Heart Disease, Emphysema, and May Complicate Pregnancy.” Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Cigarette Labels “… Smoking Causes Lung Cancer ….”
Tell students to focus on the part of the label that reads “… Smoking Causes Lung Cancer ….” Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Cigarette smoking causes lung cancer.
Label a 2 x 2 table to test the hypothesis that cigarette smoking causes lung cancer. 2 Cigarette smoking causes lung cancer. Lung Cancer No Lung Cancer Smoked Cigarettes Did Not Smoke Cigarettes a b c d Students should complete Part 2 on their Investigation 3-2: Epi Log Worksheets by labeling the 2 x 2 table to test the hypothesis “cigarette smoking causes lung cancer.” Have them compare their 2 x 2 tables with the slide. Then they should edit their tables as needed. Address misconceptions. ☼ Teacher Alert: In this curriculum, we have always labeled the 2 x 2 tables so that exposure is categorized in the 2 rows and outcome is categorized in the 2 columns. For the sake of clarity, it is probably best to be consistent with middle school students. However, it is also possible to label a 2 x 2 table so that exposure is categorized in the 2 columns and outcome is categorized in the 2 rows. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

a b c d Cigarette smoking causes lung cancer.
No Lung Cancer Smoked Cigarettes Did Not Smoke Cigarettes a b a b c d c d Next have students identify the characteristics of people in each cell of the 2 x 2 table. Review the cells in the following order: 1. Cell a: (People who smoked and developed lung cancer) 2. Cell d: (People who did not smoke and did not develop lung cancer) 3. Cell b: (People who smoked and did not develop lung cancer) 4. Cell c: (People who did not smoke and developed lung cancer) Ask students: ■ If the “cigarette smoking causes lung cancer” hypothesis were true, in what cells of the 2 x 2 table should there be people? (Cell a, people who smoked and developed lung cancer, and cell d, people who did not smoke and did not develop lung cancer) ■ Do you know of anyone who would belong in cell b, someone who smoked and did not develop lung cancer? (I have an uncle, a neighbor, a friend of the family ….) Now ask students collectively: ■ Do you know of anyone who would belong in cell c, someone who did not smoke and did develop lung cancer? (I have an uncle, a neighbor, a friend of the family ….) Next Slide Label a 2 x 2 table to test the hypothesis that cigarette smoking causes lung cancer. Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

b Cell b … anything that produces an effect.
Lung Cancer No Lung Cancer Smoked Cigarettes Did Not Smoke Cigarettes b a b c d Smoking Causes Lung Cancer Remind students that the warning label reads “… smoking causes lung cancer ….” Also remind them that a cause is “… anything that produces an effect.” Ask students: ■ If this is the case, how can you have people in cell b, those who have been exposed and do not have the outcome, and still put a label on a cigarette pack that reads “… smoking causes lung cancer …”? Explore the question. Next Slide Label a 2 x 2 table to test the hypothesis that cigarette smoking causes lung cancer. Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

b Cigarette smoking causes lung cancer.
… anything that produces an effect. Lung Cancer No Lung Cancer Smoked Cigarettes Did Not Smoke Cigarettes b a b c d Smoking Causes Lung Cancer If the exposure, and only that exposure, was the immediate cause of the outcome, it would not be possible to have people in cell b. However, there are reasons why people can be in cell b, people who have been exposed and do not have the outcome, even when the exposure causes the outcome. One reason is that the exposure may not cause the outcome immediately. If you smoked a cigarette today, would you get lung cancer today? (No) Next Slide X O Time Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

b HIV causes AIDS. … anything that produces an effect. HIV Causes AIDS
No AIDS AIDS HIV No HIV b a b c d HIV Causes AIDS As another example, the human immunodeficiency virus (HIV) is the cause of acquired immunodeficiency syndrome (AIDS), but there are people who are HIV-positive and do not have AIDS. ■ Why? (Because HIV does not immediately cause AIDS.) Next Slide HIV AIDS Time Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

… anything that produces an effect. Lung Cancer No Lung Cancer Smoked Cigarettes Did Not Smoke Cigarettes b a b c d Smoking Causes Lung Cancer Ask students: ■ Do you think this idea might apply to the “cigarette smoking causes lung cancer” hypothesis? (Yes. Some people get lung cancer 20 to 40 years after they started to smoke.) Next Slide Cigarettes Lung Cancer Time Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

b X causes O. … anything that produces an effect.
Lung Cancer No Lung Cancer Smoked Cigarettes Did Not Smoke Cigarettes b a b c d Smoking Causes Lung Cancer There is another reason why people can be in cell b. It can happen when the exposure is not necessarily enough, by itself, to produce the outcome, as, for example, when more than one exposure is needed to cause the outcome. Next Slide X + X O Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

… anything that produces an effect. Lung Cancer No Lung Cancer Smoked Cigarettes Did Not Smoke Cigarettes b a b c d Smoking Causes Lung Cancer Ask students: ■ Do you think this idea might apply to the “cigarette smoking causes lung cancer” hypothesis? (Yes. It is possible that in order for cigarette smoking to cause lung cancer, a person needs to have had another exposure such as being genetically susceptible.) Next Slide Cigarettes + Genetic Susceptibility Lung Cancer Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Measles virus causes measles. … anything that produces an effect.
No Measles Measles Measles Virus No Measles Virus b a b c d As another example, the measles virus is the cause of measles, but not everyone who is exposed to the virus develops measles. ■ Why? (Some people are immune because they have previously had measles or because they have been immunized with a measles vaccine.) ☼ Teacher Alert: The measles vaccine is usually combined with vaccines for mumps and rubella. Next Slide + No Immunity Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

X causes O. X O 1. 2. 3. Time a b c d Lung Cancer No Lung Cancer Smoked Cigarettes Did Not Smoke Cigarettes b Time + X X O Summarize how it is possible for an exposure to produce an outcome and for cell b to still have people in it, that is, those who were exposed and who do not have the outcome. ■ Why? We can list three reasons: 1. The exposure does not immediately cause the outcome. 2. The exposure is not the only exposure needed to produce the outcome. Both reasons. Next Slide Time + X X O Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

c Cell c … anything that produces an effect.
Lung Cancer No Lung Cancer … anything that produces an effect. Smoking Causes Lung Cancer Smoked Cigarettes Did Not Smoke Cigarettes a b c d c Cigarettes X O Lung Cancer Asbestos Now direct attention to cell c, where people who have not been exposed have the outcome, that is, where people who did not smoke and have developed lung cancer would be. Remind students that the warning label reads “… smoking causes lung cancer ….” Also remind them that a cause is “… anything that produces an effect.” Ask students: ■ If this is the case, how can you have people in cell c and still put a label on a cigarette pack that reads “… smoking causes lung cancer …”? Tell students to think about this diagram of the relationship between an exposure and an outcome. ■ If the red X (exposure) was cigarette smoking, how would people get in cell c? (There are other causes of the same outcome. The blue X [exposure] and the yellow X [exposure] can also cause the outcome.) ■ Do you think this might apply to the “cigarette smoking causes lung cancer” hypothesis? (Yes. We know that there are other exposures that cause lung cancer—for example, asbestos and radon.) Next Slide Radon Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Label the 2 x 2 table and identify the cells in which there would be people, if the exposure caused the disease. 3 X causes O. O No O X No X a b c d Students should complete Part 3 on their Investigation 3-2: Epi Log Worksheets by labeling the cells of the 2 x 2 table and identifying in which cells there would be people if an exposure caused a disease or other health-related outcome. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Compare your answers to Parts 1 and 3.
4 X causes O. O No O X No X a b c d Students should complete Part 4 on their Investigation 3-2: Epi Log Worksheets by comparing their answers with those for Parts 1 and 3. ☼ Teacher Alert: At this point in the investigation, we expect students to conclude that the people would be in cell a, that is, people who are exposed would have the outcome, and in cell d, that is, people who are not exposed would not have the outcome. In addition, we expect students to also identify cells b and c. They should appreciate why it is possible to have people in cell b, people who are exposed and do not have the outcome, and in cell c, people who are not exposed and have the outcome, and still be able to conclude that the exposure causes the outcome. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Have you identified cell a? O No O X No X a b c d Have you identified cells b and c? Have you identified cell d? Ask students: ■ Can you describe the differences in your responses to the class? ■ Use the following questions as a guide to judge the quality of your work: □ Have you identified cell a? □ Have you identified cell d? □ Have you identified cells b and c? Next Slide Compare your answers to Parts 1 and 3. Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Describe how you can have people in cells b and c and still put a label on a pack of cigarettes that reads “… smoking causes lung cancer ….” 5 Cigarette smoking causes lung cancer. Have you mentioned time delay between exposure and outcome? Have you mentioned the possible need for another exposure? SURGEON GENERAL’S WARNING: Smoking Causes Lung Cancer, Heart Disease, Emphysema, and May Complicate Pregnancy Students should complete Part 5 on their Investigation 3-2: Epi Log Worksheets by describing how there can be people in cells b and c and a label can still be put on a cigarette pack that reads “… smoking causes lung cancer ….” Ask students: ■ Use the following questions as a guide to judge the quality of your work: □ Have you mentioned time delay between exposure and outcome? □ Have you mentioned the possible need for another exposure? ■ Keeping in mind the definition of ‘cause’, anything that produces an effect, is the label, “… smoking causes lung cancer ….” justified? (Yes, cigarette smoking does produce an effect.) Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Lack of fitness and physical activity causes heart attacks.
Label a 2 x 2 table and identify the cells in which there would be people if the exposure caused the disease. 6 Lack of fitness and physical activity causes heart attacks. a b c d This diagram depicts how different exposures, including a lack of fitness and physical activity, cause the outcome, heart attack. Students should complete Part 6 on their Investigation 3-2: Epi Log Worksheets by labeling the 2 x 2 table to test the hypothesis that a lack of fitness and physical activity causes heart attacks and by identifying the cells in which there would be people if this exposure caused this outcome. Compare students’ answers with the next slide. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

a b c d 6 Lack of fitness and physical activity causes heart attacks.
No Heart Attack Lack of Fitness No Lack of Fitness a b a b c d c d Cell a: (People who lack fitness and had a heart attack) Cell d: (People who are fit and did not have a heart attack) But also some in Cell b: (People who lack fitness but have not had a heart attack; maybe they have been unfit for too short a time.) Cell c: (People who are fit and had a heart attack; other exposures cause heart attacks besides lack of fitness.) Next Slide Label a 2 x 2 table and identify the cells in which there would be people, if the exposure caused the disease. Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Epi Speak Epi Speak Multiple Causes A combination of causes or an alternative cause that produces the effect. Ask students to find “Multiple causes” in the Epi Speak list. Review its definition. ☼ Teacher Alert: In the web of causation depicted on the previous slide, a lack of fitness and physical activity is one of a combination of causes producing heart attack. Therefore, a lack of fitness and physical activity is not the cause of heart attack. It is a cause of heart attack. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

7 Label a 2 x 2 table and identify the cells in which there would be people if the exposure caused the disease. Lack of supervision of small children causes lead poisoning. a b c d This diagram depicts how different exposures, including a lack of supervision of small children, cause the outcome, lead poisoning. Students should complete Part 7 on their Investigation 3-2: Epi Log Worksheets by labeling the 2 x 2 table to test the hypothesis that a lack of supervision of small children causes lead poisoning and by identifying the cells in which there would be people if this exposure caused this outcome. Compare students’ answers with the next slide. Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

7 Lack of supervision of small children causes lead poisoning. Lead Poisoning No Lead Poisoning Lack of Supervision No Lack of Supervision a b a b c d c d Cell a: (Children who lack supervision and have lead poisoning) Cell d: (Children who have supervision and do not have lead poisoning) But also some in Cell b: (Children who lack supervision but do not have lead poisoning; there may not be lead paint in the home.) Cell c: (Children who have supervision and have lead poisoning; there may be lead-contaminated water due to lead in pipes.) ☼ Teacher Alert: In the web of causation depicted on the slide, lack of supervision of small children is one of a combination of causes producing lead poisoning. Therefore, a lack of supervision of small children is not the cause but a cause of lead poisoning. Next Slide Label a 2 x 2 table and identify the cells in which there would be people if the exposure caused the disease. Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Explanations for Finding an Association
1. Cause 2. 3. 4. 5. Why would an exposure and an outcome turn up together? Students now know from Investigation 3-2: Cause that one of the reasons why epidemiologists can find an association between an exposure and an outcome—that is, they turn up together—is that the exposure causes the outcome. The exposure actually produces the effect of the outcome. Point out that when an association is found, the causal explanation is often the first one we consider. Remind students when they read about a tie, link, relationship, or association in the news, they need to ask the following: ■ What does it mean? ■ Is the association causal? ■ Did the exposure and the disease turn up together because the exposure produced the disease? Next Slide Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Investigation 3-2 has ended.
Cause Investigation has ended. CDC In the next investigation, students will explore another possible explanation for finding an association between an exposure and an outcome: chance. This concludes Investigation 3-2: Cause and students can now put away their Epi Logs. Intro to Epidemiology – Investigation 3-2: Cause Investigation 3-2

Cause Is this association causal?

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