The 2x2 Table Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Where are we and where are we going? Detectives in the Classroom - Investigation 2-1: The 2x2 Table 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? 5. Did the prevention strategy work?

1 How is this disease distributed? Hypotheses 3 Is the association causal? 4 What should be done to prevent the disease? 5 Did the prevention strategy work? Where are we and where are we going? What’s my hypothesis? 2 Is there an association? Did the exposure and the disease turn up together? Detectives in the Classroom - Investigation 2-1: The 2x2 Table

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. How is this disease distributed and what hypotheses might explain that distribution? Review Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Hypothesis Testing Hypotheses Detectives in the Classroom - Investigation 2-1: The 2x2 Table Formulate Descriptive Epidemiology Test Analytical Epidemiology

Epi Talk A study designed to investigate hypothesized causal relationships. Tries to determine why disease is occurring. Tests hypotheses. Epi Talk Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Epidemiologist Drug Company Oily skin AcneMed AcneMed prevents acne. Acne Oily skin causes acne. Scenario Detectives in the Classroom - Investigation 2-1: The 2x2 Table

100 teenagers Sample Population All Teenagers Trial 1 10 teenagers had acne. for 6 months “AcneMed Prevents Acne.” Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Epi Log Worksheet

AcneMed Acne No Acne Total How is acne distributed among the 100 teenagers who took AcneMed? Trial 1 10 Teenagers Had Acne Detectives in the Classroom - Investigation 2-1: The 2x2 Table 1

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. Risk 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. Population Event Denominator Numerator Express It in Numbers Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Epi Talk Detectives in the Classroom - Investigation 2-1: The 2x2 Table Risk Epi Talk 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.

AcneMed Acne No Acne Total or 10 % Trial 1 Acne Risk Express It in Numbers 2 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

“AcneMed Prevents Acne.” Inference 100 teenagers 10/100 or 10% Sample Population All Teenagers Trial 1 Process of predicting from what is observed Observed Not Observed to what is not observed. Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Inference Epi Talk 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. Epi Talk Detectives in the Classroom - Investigation 2-1: The 2x2 Table

AcneMed Acne No Acne Total Acne Risk or 10 % Maybe they had acne when the experiment began. Maybe they said they took AcneMed but did not. Maybe they took AcneMed but not enough to prevent acne “AcneMed Prevents Acne.” Detectives in the Classroom - Investigation 2-1: The 2x2 Table If AcneMed prevents acne, why did anyone get acne? Shouldn’t the risk of acne have been 0%?

AcneMed Acne No Acne Total Acne Risk or 10 % Maybe taking AcneMed does not prevent acne What needs to be done? Maybe those 90 teenagers would not have developed acne even if they had not taken AcneMed. Detectives in the Classroom - Investigation 2-1: The 2x2 Table “AcneMed Prevents Acne.” If AcneMed prevents acne, why did anyone get acne? Shouldn’t the risk of acne have been 0%?

Control Group Epi Talk People who participate in a trial, but do not get the treatment. Epi Talk Detectives in the Classroom - Investigation 2-1: The 2x2 Table People whose results are compared to the group that was treated.

“AcneMed Prevents Acne.” Inference Population All Teenagers Trial 1 Not Observed 100 teenagers 10/100 or 10% Sample Observed ? / 100 or ? % 100 teenagers Sample No AcneMed AcneMed Not Observed Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Epi Teams Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Experimental Group AcneMed Acne No Acne Total Acne Risk or 10 % Trial 1 Detectives in the Classroom - Investigation 2-1: The 2x2 Table 3

Control Group AcneMed Acne No Acne Total Acne Risk or 10 % No AcneMed 100 Trial 1 ? 100 or ? % Detectives in the Classroom - Investigation 2-1: The 2x2 Table 3

Exposures Epi Talk Detectives in the Classroom - Investigation 2-1: The 2x2 Table Factors with which individuals come in contact.

Outcomes Epi Talk Detectives in the Classroom - Investigation 2-1: The 2x2 Table All the possible results that occur because of exposure to a causal factor.

2 Rows, 2 Columns, 4 Cells AcneMed Acne No Acne Total No AcneMed 100 ab cd 2x2 Table Detectives in the Classroom - Investigation 2-1: The 2x2 Table Exposure Outcome / Disease

Exposed Disease No Disease Total Not Exposed ab dc People who are exposed ab 2x2 Table 4 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Exposed Disease No Disease Total Not Exposed ab dc People who are exposed and have the disease a 2x2 Table 5 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Exposed Disease No Disease Total Not Exposed ab dc People who are not exposed and do not have the disease d 2x2 Table 6 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Exposed Disease No Disease Total Not Exposed ab dc People who do not have the disease and are not exposed d 2x2 Table 7 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Exposed Disease No Disease Total Not Exposed ab dc People who are not exposed dc 2x2 Table 8 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Exposed Disease No Disease Total Not Exposed ab dc People who do not have the disease d b 2x2 Table 9 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Exposed Disease No Disease Total Not Exposed ab dc People who are exposed and do not have the disease b 2x2 Table 10 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Exposed Disease No Disease Total Not Exposed ab dc People who have the disease a c 2x2 Table 11 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Exposed Disease No Disease Total Not Exposed ab dc c People who are not exposed and have the disease 2x2 Table 12 Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Epidemiology Epi Talk The study of how and why diseases or other health- related conditions are distributed in a population the way they are; in other words, why some people get sick and others do not. Review Detectives in the Classroom - Investigation 2-1: The 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 No AcneMed 100 2x2 Table How does this definition apply to the 2x2 table? The 2x2 Table Detectives in the Classroom - Investigation 2-1: The 2x2 Table

AcneMed Acne No Acne Total No AcneMed 100 Epidemiology The study of how disease is distributed in populations and of the exposures that cause that distribution. 2x2 Table How does this definition apply to the 2x2 table? The 2x2 Table Detectives in the Classroom - Investigation 2-1: The 2x2 Table

AcneMed Acne No Acne Total No AcneMed 100 2x2 Table Epidemiology The study of how disease is distributed in populations and of the exposures that cause that distribution. Disease No Disease How does this definition apply to the 2x2 table? Disease The 2x2 Table Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Disease 2x2 Table How does this definition apply to the 2x2 table? Epidemiology The study of how disease is distributed in populations and of the exposures that cause that distribution. AcneMed Disease No Disease Total No AcneMed 100 Exposed Not Exposed Exposures The 2x2 Table Detectives in the Classroom - Investigation 2-1: The 2x2 Table

AcneMed Total No AcneMed 2x2 Table How does this definition apply to the 2x2 table? Epidemiology The study of how disease is distributed in populations and of the exposures that cause that distribution. ab cd Acne No Acne The 2x2 Table Detectives in the Classroom - Investigation 2-1: The 2x2 Table

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 How Is Acne Distributed? Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Investigation 2-1 has ended. The 2x2 Table Detectives in the Classroom - Investigation 2-1: The 2x2 Table