# Calculating Odds Ratio: Creating a 2×2 Contingency Table.

Calculating Odds Ratio: Creating a 2×2 Contingency Table.

Data can be qualitative or quantitative. Qualitative data is helpful to generate a hypothesis and gather information if little is known about an expected association. Focus groups, key informant interviews, and case studies are types of qualitative data collection methods used to identify common themes from which to build a hypothesis. Quantitative data collection and analysis is used to test a hypothesis and make comparisons to determine the direction and strength of a potential association. The Behavioral Risk Factor Surveillance System (BRFSS) is cross-sectional panel survey used to collect quantitative data on adult behaviors and risk factors. It is one of the largest U.S. health data collection efforts. The data can be used to analyze associations on a state or country level. Follow the steps to obtain a 2×2 contingency table (also known as a “cross tabulation”) crossing binge drinking with depression.
1. Retrieve the “BRFSS Web-Enabled Analysis Tool” resource provided in the Topic Materials.
2. Select “Cross Tabulation.”
3. Select “2015” for the year.
4. Select “Arizona” for the state.
5. Select “Alcohol Consumption: Binge drinkers (males having five or more drinks on one occasion, females having four or more drinks on one occasion)” for Step 2 Select Row.
6. Select “Chronic Health Conditions: Ever diagnosed with a depressive disorder, including depression, major depression, dysthymia, or minor depression” for Step 3 Select Column.
7. Skip Steps 4 and 5.
8. Select “Sample Size” for Step 6 Select Statistics and run the report for the cross tabulation.
Part 1
Using the data from the cross tabulation results, calculate the odds ratio for depression among those exposed to binge drinking. Interpret the odds ratio and discuss if the odds ratio is a good estimate of the relative risk in this situation. Why or why not? Show your 2×2 table and all calculations. Present or describe the formula you used to arrive at your answer.
Part 2
Use the Topic Material, “BRFSS Web-Enabled Analysis Tool,” located on the CDC website, and run a report for two variables of interest to you. Create a 2×2 table and calculate the odds ratio for this association. Interpret the odds ratio and discuss the public health importance of the association. Show your 2×2 table. Present or describe the formula you used to arrive at your answer.
Refer to the “Creating a 2×2 Contingency Table” resource for guidance in creating 2×2 contingency tables.
General Requirements
APA style is required for references, and solid academic writing is expected.
This assignment uses a rubric. Please review the rubric prior to beginning the assignment to become familiar with the expectations for successful completion.

Creating a 2×2 Contingency Table

Creating a 2×2 contingency table is very useful in calculating a variety of public health measurements, including sensitivity and specificity, negative and positive predictive value, risk ratios, attack rate ratios, and odds ratios.

A 2×2 table is actually a 3×3 table when you include the rows and columns for the totals. If you are setting up a table to measure the sensitivity and specificity of a test or its negative and positive predictive values, you should put the test results on the y-axis (rows) and the actual presence of disease on the x-axis (columns).

 Disease No Disease Total Test (+) (a) (b) a + b Test (-) (c) (d) c + d Total a + c b + d a + b + c + d

The highlighted section is where you will enter the data for each corresponding cell. You can set up the table switching the rows and columns but you will generally see them set up in this format with test results on the y-axis and disease on the x-axis.

Setting up a table to measure the association of a risk factor or exposure is similar, with the outcome or disease on the x-axis and the presence of the risk factor or exposure on the y-axis.

 Disease No Disease Total Exposure (+) (a) (b) a + b Exposure (-) (c) (d) c + d Total a + c b + d a + b + c + d

Note: You can set up the table differently but you will need to be cognizant of which numbers you are putting in your numerator and denominator for the measure you are calculating. For example:

 Exposure (+) Exposure (-) Total No Disease (b) (d) b + d Disease (a) (c) a + c Total a + b b + c a + b + c + d

Calculating Odds Ratio: Creating a 2×2 Contingency Table.