Intro to Epidemiology - Investigation 2-1: The 2x2 Table

Intro to Epidemiology - Investigation 2-1: The 2x2 Table
In Investigation 2-1: The 2 x 2 Table, students will examine the results of a hypothetical study to determine if a medication prevents acne. In this investigation, students discover that a scientific experiment needs to examine not only a group of people who are exposed to a medication but also a group not exposed to it, called a control group. Students construct 2 x 2 tables and, in studying how an exposure and an outcome (disease) are distributed, they see that every person in a study population fits into one of the four cells of the 2 x 2 table. Students also learn that the way an exposure and an outcome are distributed in a group of people can be expressed mathematically. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Where are we and where are we going?
1. How is this disease distributed and what hypotheses might explain that distribution? 2. Is there an association between the hypothesized cause and the disease? 3. Is the association causal? 4. What should individuals and society do when preventable causes of disease are found? Remind students that they have learned how epidemiologists answer the first Essential Question: How is this disease distributed and what hypotheses might explain that distribution? In the Module 2 investigations, students will now learn how to answer epidemiologists’ second Essential Question: “Is there an association between the hypothesized cause and the disease?” In the Module 3, 4, and 5 investigations, they will learn how epidemiologists answer the following questions, respectively: Is the association causal? What should individuals and society do when preventable causes of disease are found? Did the prevention strategy work? Next Slide 5. Did the prevention strategy work? Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Where are we and where are we going?
2 Is there an association? Did the exposure and the disease turn up together? 1 How is this disease distributed? Hypotheses 3 Is the association causal? What’s my hypothesis? 4 What should be done to prevent the disease? Tell students that this Concept Map is another way to look at the Essential Questions. In Module 1 investigations, students learned how epidemiologists answer the question “How is this disease distributed?” or “What’s my hypothesis?” And now, in Module 2 investigations, students will learn how epidemiologists answer the question “Is there an association?” or “Did the exposure and the disease turn up together?” Next Slide 5 Did the prevention strategy work? Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Review How is this disease distributed and what hypotheses might explain that distribution? Health-related conditions and behaviors are not distributed uniformly in a population. Each has a unique descriptive epidemiology that can be discovered by identifying how it is distributed in a population in terms of person, place, and time. Descriptive epidemiology provides clues for formulating hypotheses. Referring to students’ Concept Maps from Module 1, which are posted in the classroom, remind students that they have developed the first Enduring Understanding: “Health-related conditions and behaviors are not distributed uniformly in a population. Each has a unique descriptive epidemiology that can be discovered by identifying how it is distributed in a population in terms of person, place, and time. Descriptive epidemiology provides clues for formulating hypotheses.” They are on their way to being able to answer the Essential Question: “How is this disease distributed and what hypotheses might explain that distribution?” Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Testing Hypotheses Formulate Descriptive Epidemiology Test Analytical Epidemiology Hypothesis Reiterate that hypotheses are educated guesses. They are unproven ideas, based on observation or reasoning, that can be proven or disproven through investigation. Students should know from their Module 1 Investigations that clues for formulating hypotheses can be found by observing an outcome’s descriptive epidemiology, the way it is distributed in a population of people, in terms of person, place, and time. In addition to formulating hypotheses, epidemiologists, disease detectives, also test their hypotheses. The hypothesis-testing part of epidemiology is called analytical epidemiology. In other words, descriptive epidemiology helps formulate hypotheses and analytical epidemiology helps test them. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Epi Speak Epi Speak Analytical Epidemiology A study designed to investigate hypothesized causal relationships. Tries to determine why disease is occurring. Tests hypotheses. Ask students to find “Analytical epidemiology” in the Epi Speak list. Review its definition. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Scenario Acne Oily skin Oily skin causes acne. Epidemiologist AcneMed Drug Company Present the following scenario: You are an epidemiologist working for a drug company. You have reviewed the descriptive epidemiology of acne, found that it is more likely to occur among people who have oily skin, and formulated this hypothesis: “Oily skin causes acne.” Chemists, who also work for the drug company, have developed a medicine, called AcneMed, that makes skin less oily and have formulated another hypothesis: “AcneMed prevents acne.” It is your responsibility to test the hypothesis “AcneMed prevents acne.” Next Slide AcneMed prevents acne. Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

“AcneMed Prevents Acne.”
Trial 1 Population All Teenagers 100 teenagers Sample for 6 months 10 teenagers had acne. Tell students that they have tested the hypothesis in what you call “Trial 1.” From a population of all teenagers, they selected a sample of 100 teenagers. They tested the hypothesis by having these 100 teenagers take AcneMed once a day for 6 months. After taking AcneMed for 6 months, only 10 of the 100 teenagers developed acne. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Epi Log Worksheet Give each student an Investigation 2-1: Epi Log Worksheet. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

10 Teenagers Had Acne Trial 1 No Acne Acne Total AcneMed 10 90 100 How is acne distributed among the 100 teenagers who took AcneMed? Students should complete Part 1 of their Investigation 2-1: Epi Log Worksheets by placing the results of Trial 1 in the table. Discuss their answers. Probe until they agree that the table should look as depicted above. Ask students: ■ Can you describe how acne was distributed among the 100 people who took AcneMed? (Although “some,” “not many,” and “most didn’t” are accurate, try to get the students to use numbers.) Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Express It in Numbers Risk A measure of how often an event occurs in a defined population in a defined period of time. It consists of a numerator and a denominator. Numerator Denominator The numerator is the number of people in the population who experience the event and the denominator is the total number of people in the population. Event One way epidemiologists measure how a disease is distributed and express it in numbers is by calculating a risk. Explain the definition of a risk and discuss as needed. A risk is a measure of how often an event occurs in a defined population in a defined period of time. It consists of a numerator and a denominator. The numerator is the number of people in the population who experience the event and the denominator is the total number of people in the population. Next Slide Population Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Epi Speak Epi Speak Risk A measure of how often an event occurs in a defined group of people in a defined period of time. The likelihood of developing a disease. Ask students to find “Risk” in the Epi Speak list. Review its definition. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Express It in Numbers Trial 1 No Acne Acne Risk Acne Total 10 or 10 % AcneMed 10 90 100 100 Students should complete Part 2 of their Investigation 2-1: Epi Log Worksheets by calculating the risk of acne among the 100 teenagers who took AcneMed during the 6-month period. (In this case, the denominator is the 100 people who took AcneMed, and the numerator is the 10 occurrences of the event—developing acne.) Discuss students’ answers. ☼ Teacher Alert: If necessary, review the process of changing a fraction into a percent. Ask students: ■ Can you explain what the 10% risk of acne tells about the hypothesis “AcneMed prevents acne”? (AcneMed seems to have prevented 90% of the people from developing acne. But 10% of the population who took AcneMed still developed acne.) Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Trial 1 Not Observed to what is not observed. Population Inference Process of predicting from what is observed Observed Sample 100 teenagers 10/100 or 10% All Teenagers When students answered the question “What does the 10% risk of acne tell you about the hypothesis ‘AcneMed prevents acne’?” they made an inference. Review the definition of inference with the class. An inference is the process of predicting from what is observed (the 100 teenagers who were in the study sample for Trial 1) back to the population of those who were not observed (all the teenagers in the population who were not in Trial 1). Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Epi Speak Epi Speak Inference Process of predicting from what is observed in a sample to what is not observed in a population. To generalize back to the source population. Ask students to find “Inference” in the Epi Speak list. Review its definition. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

If AcneMed prevents acne, why did anyone get acne? Shouldn’t the risk of acne have been 0%? No Acne Acne Risk Acne Total 10 100 10 % AcneMed 10 90 100 or 100 Maybe they had acne when the experiment began. Ask students: ■ If AcneMed prevents acne, why did some of the teenagers develop acne? Shouldn’t the risk of acne have been 0%? Discuss possibilities with the class. Then consider what might be done to eliminate each possibility. Make sure to mention the following if students have not done so: ■ Maybe some of the teenagers had acne when the experiment began. (Teenagers with acne should have been eliminated before the study began.) ■ Maybe some of the teenagers said they took AcneMed but did not. (Participants’ urine should have been tested for AcneMed to find out if they were actually taking the medication.) ■ Maybe some of the teenagers took AcneMed, but it was not enough to prevent acne. (Participants should have been instructed to take two AcneMed capsules daily and their urine should have been tested each day to determine whether they were taking the prescribed amount.) Next Slide Maybe they said they took AcneMed but did not. Maybe they took AcneMed but not enough to prevent acne. Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

If AcneMed prevents acne, why did anyone get acne? Shouldn’t the risk of acne have been 0%? No Acne Acne Risk Acne Total 10 100 10 % AcneMed 10 90 100 or 100 What needs to be done? Maybe taking AcneMed does not prevent acne. Students should consider one more possibility: Maybe taking AcneMed does not prevent acne. Discuss until students see the possibility that those 90 teenagers would not have developed acne even if they had not taken AcneMed. Ask students: ■ What needs to be done to find out if AcneMed really worked? ■ What needs to be done to determine if the 90 people would not have gotten acne even if they had not taken AcneMed? Explore these questions until students conclude that they need to see what happens to a group of teenagers who do not take AcneMed and see how many develop acne in that group. Then they can compare the risks of acne in both groups. ☼ Teacher Alert: Do not stop exploring until students uncover both parts of the above answer. (They need to see what happens to another group of teenagers who do not take AcneMed and see how many develop acne. Then they can compare the acne risks in both groups.) Next Slide Maybe those 90 teenagers would not have developed acne even if they had not taken AcneMed. Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Epi Speak Epi Speak Control Group People who participate in a trial, but do not get the treatment. People whose results are compared to the group that was treated. Tell students that the other group of teenagers, those who do not take AcneMed, is called a control group, the subjects with whom a comparison is made. Ask students to find “Control group” in the Epi Speak list. Review its definition. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Trial 1 Population Inference 100 teenagers Sample No AcneMed Sample AcneMed 100 teenagers 10/100 or 10% All Teenagers Ask students: ■ How would you change this slide to depict a control group? Keep asking until students decide to put a control group of 100 teenagers who do not take AcneMed on the “Observed” side of the slide. Then a risk of acne for the control group is calculated and compared to the risk of acne in the group treated with AcneMed. Next Slide Not Observed Not Observed ? / 100 or ? % Observed Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

3 Experimental Group Trial 1 No Acne Acne Risk Acne Total 10 AcneMed 10 90 100 or 10 % 100 Students should complete Part 3 of their Investigation 2-1: Epi Log Worksheets by extending the table to include a control group of 100 teenagers. Have students share and compare their tables with the other members of their Epi Team. Encourage students to edit their responses as needed. Ask one member of each Epi Team to draw his or her table on the board. Share, compare, and edit as needed. Compare students’ responses with those shown on the next slide. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

3 Control Group Trial 1 No Acne Acne Risk Acne Total 10 10 % AcneMed 10 90 100 or 100 No AcneMed ? 100 or ? % 100 Have students edit their tables as needed. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Epi Speak Epi Speak Exposures Factors with which individuals come in contact. Ask students to find “Exposures” in the Epi Speak list. Review its definition. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Epi Speak Epi Speak Outcomes All the possible results that occur because of exposure to a causal factor. Ask students to find “Outcomes” in the Epi Speak list. Review its definition. Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

2 Rows, 2 Columns, 4 Cells Outcome / Disease 2x2 Table No Acne Acne Total Exposure a b AcneMed 10 90 100 c d No AcneMed 100 Explain that what the students have drawn is called a 2 x 2 table. It has 2 rows, one for the 100 teenagers who were exposed to AcneMed and another for the 100 who were not. And it has 2 columns, one for the teenagers who developed acne and the other for those who did not. The 2 rows and 2 columns cross each other and form 4 cells. These cells are labeled a, b, c, and d, as shown on the slide. The 2 x 2 table is an important tool for an epidemiologist, a disease detective, because it depicts the distribution of an exposure and an outcome in a population at the same time. Ask students: ■ Can you describe the people in cell a? Give students time to figure out the correct answer. (People who are exposed and have the outcome) ■ Can you describe the people in cell b? (People who are exposed and do not have the outcome) ■ Can you describe the people in cell c? (People who are not exposed and have the outcome) ■ Can you describe the people in cell d? (People who are not exposed and do not have the outcome) Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

4 2x2 Table No Disease Disease Total a b Exposed a b c d Not Exposed Students should complete Part 4 of their Investigation 2-1: Epi Log Worksheets by identifying the cell or cells in the 2 x 2 table in which the following group of people belongs: ■ People who are exposed. Have students share and compare their answers with the other members of their Epi Team. Compare students’ answers with the correct response. (Cells a and b) Address misconceptions. ☼ Teacher Alert: As a variation, have an Epi Team Challenge in which the teams practice identifying which cell or cells in the 2 x 2 table groups of people belong in. Give each Epi Team a set of four challenge cards (a, b, c, and d) and ask each Epi Team to hold up the card that identifies the cell or cells in which the groups belong. Next Slide People who are exposed Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

2x2 Table 5 a People who are exposed and have the disease Total
No Disease Disease Total a Exposed a b c d Not Exposed Students should complete Part 5 of their Investigation 2-1: Epi Log Worksheets by identifying the cell or cells in the 2 x 2 table in which the following group of people belongs: ■ People who are exposed and have the disease. Have students share and compare their answers with the other members of their Epi Team. Compare students’ answers with the correct response. (Cell a) Address misconceptions. Next Slide People who are exposed and have the disease Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

2x2 Table 6 d People who are not exposed and do not have the disease
No Disease Disease Total Exposed a b c d d Not Exposed Students should complete Part 6 of their Investigation 2-1: Epi Log Worksheets by identifying the cell or cells in the 2 x 2 table in which the following group of people belongs: ■ People who are not exposed and do not have the disease. Have students share and compare their answers with the other members of their Epi Team. Compare students’ answers with the correct response. (Cell d) Address misconceptions. Next Slide People who are not exposed and do not have the disease Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

2x2 Table 7 d People who do not have the disease and are not exposed
No Disease Disease Total Exposed a b c d d Not Exposed Students should complete Part 7 of their Investigation 2-1: Epi Log Worksheets by identifying the cell or cells in the 2 x 2 table in which the following group of people belongs: ■ People who do not have the disease and are not exposed. Note that this is the same as Part 6 but reversed. Have students share and compare their answers with the other members of their Epi Team. Compare students’ answers with the correct response. (Cell d) Address misconceptions. Next Slide People who do not have the disease and are not exposed Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

2x2 Table 8 c d People who are not exposed Total Exposed Not Exposed
No Disease Disease Total Exposed a b c c d d Not Exposed Students should complete Part 8 of their Investigation 2-1: Epi Log Worksheets by identifying the cell or cells in the 2 x 2 table in which the following group of people belongs: ■ People who are not exposed. Have students share and compare their answers with the other members of their Epi Team. Compare students’ answers with the correct response. (Cells c and d) Address misconceptions. Next Slide People who are not exposed Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

2x2 Table 9 b d People who do not have the disease Total Exposed
No Disease Disease Total b Exposed a b c d d Not Exposed Students should complete Part 9 of their Investigation 2-1: Epi Log Worksheets by identifying the cell or cells in the 2 x 2 table in which the following group of people belongs: ■ People who do not have the disease. Have students share and compare their answers with the other members of their Epi Team. Compare students’ answers with the correct response. (Cells b and d) Address misconceptions. Next Slide People who do not have the disease Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

2x2 Table 10 b People who are exposed and do not have the disease
No Disease Disease Total b Exposed a b c d Not Exposed Students should complete Part 10 of their Investigation 2-1: Epi Log Worksheets by identifying the cell or cells in the 2 x 2 table in which the following group of people belongs: ■ People who are exposed and do not have the disease. Have students share and compare their answers with the other members of their Epi Team. Compare students’ answers to correct response. (Cell b) Address misconceptions. Next Slide People who are exposed and do not have the disease Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

2x2 Table 11 a c People who have the disease Total Exposed Not Exposed
No Disease Disease Total a Exposed a b c c d Not Exposed Students should complete Part 11 of their Investigation 2-1: Epi Log Worksheets by identifying the cell or cells in the 2 x 2 table in which the following group of people belongs: ■ People who have the disease. Have students share and compare their answers with the other members of their Epi Team. Compare students’ answers with the correct response. (Cells a and c) Address misconceptions. Next Slide People who have the disease Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

2x2 Table 12 c People who are not exposed and have the disease Total
No Disease Disease Total Exposed a b c c d Not Exposed Students should complete Part 12 of their Investigation 2-1: Epi Log Worksheets by identifying the cell or cells in the 2 x 2 table in which the following group of people belongs: ■ People who are not exposed and have the disease. Compare students’ answers with the correct response. (Cell c) Address misconceptions. Next Slide People who are not exposed and have the disease Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

The 2x2 Table 2x2 Table Epidemiology
The study of how disease is distributed in populations and of the exposures that cause that distribution. AcneMed Acne No Acne Total 100 90 10 No AcneMed 2x2 Table Tell students to consider how the three parts of this definition of epidemiology apply to the 2 x 2 table. Next Slide How does this definition apply to the 2x2 table? Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

The 2x2 Table 2x2 Table Epidemiology
The study of how disease is distributed in populations and of the exposures that cause that distribution. 2x2 Table No Acne Acne Total AcneMed 10 90 100 No AcneMed 100 Ask students: ■ How does the phrase “in populations” apply to the 2 x 2 table? Probe until students conclude that the populations are the groups of people who were studied (in this case, the 100 teenagers who took AcneMed, the experimental group, and the 100 teenagers who did not take AcneMed, the control group). Next Slide How does this definition apply to the 2x2 table? Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

The 2x2 Table Disease 2x2 Table Epidemiology
The study of how disease is distributed in populations and of the exposures that cause that distribution. 2x2 Table No Disease No Acne Acne Disease Total AcneMed 10 90 100 No AcneMed 100 Ask students: ■ How does the phrase “how disease is distributed” apply to the 2 x 2 table? Probe until students conclude that the 2 columns of the 2 x 2 table depict how disease is distributed in populations. Next Slide How does this definition apply to the 2x2 table? Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

The 2x2 Table Disease 2x2 Table Epidemiology
The study of how disease is distributed in populations and of the exposures that cause that distribution. 2x2 Table No Disease Disease Total Exposures AcneMed Exposed 10 90 100 No AcneMed Not Exposed 100 Ask students: ■ How does the phrase “exposures that cause that distribution” apply to the 2 x 2 table? Probe until students conclude that the 2 rows of the 2 x 2 table depict the exposures that may influence or determine that distribution. ☼ Teacher Alert: An exposure can be hypothesized to be beneficial, as is the case with AcneMed. Exposures can also be hypothesized to be harmful, which will be addressed in Investigation And sometimes an exposure is found to be both beneficial and harmful, as is the case with birth control pills, which reduce the risk of pregnancy and increase the risk of blood clots, stroke, and heart attack. Next Slide How does this definition apply to the 2x2 table? Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

The 2x2 Table Epidemiology
The study of how disease is distributed in populations and of the exposures that cause that distribution. 2x2 Table No Acne Acne Total a b AcneMed c d No AcneMed Remind students that the 2 x 2 table is an important tool for an epidemiologist, a disease detective, because it depicts the distribution of exposure and disease in a population at the same time. Once again, ask students: ■ Can you describe the people in cell a? (People who are exposed and have the disease or outcome) ■ Can you describe the people in cell b? (People who are exposed and do not have the disease or outcome) ■ Can you describe the people in cell c? (People who are not exposed and have the disease or outcome) ■ Can you describe the people in cell d? (People who are not exposed and do not have the disease or outcome) Next Slide How does this definition apply to the 2x2 table? Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

How Is Acne Distributed?
When you can measure what you are Speaking about, and express it in numbers, you know something about it. But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind. Lord Kelvin Discuss students’ interpretation of the quote shown on the slide. Ask students: ■ How does this quote apply to what you have learned in this investigation? Next Slide Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

I can see you. Tell students that in the next investigation, they will continue testing the hypothesis that AcneMed prevents acne in Trials 2, 3, and 4. This concludes Investigation 2-1: The 2 × 2 Table and students can now put away their Epi Logs. Intro to Epidemiology - Investigation 2-1: The 2x2 Table Investigation 2-1

Intro to Epidemiology - Investigation 2-1: The 2x2 Table

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Intro to Epidemiology - Investigation 2-1: The 2x2 Table

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