# How to calculate p value from odds ratio

By | 02.06.2021 Odds Ratio Calculator

You can use Fisher's exact test, which inputs a contingency table and outputs a p-value, with a null hypothesis that the odds ratio is 1 and an alternative hypothesis that the odds ratio is not equal to 1. (tab p-value = # alternative hypothesis: true odds ratio is . If a p -value is needed instead of a confidence interval, it can be obtained in one of the following ways. Beginning in SAS TS1M3, odds ratio estimates and p -values for a predictor can be obtained by adding the ORPVALUE option in the MODEL statement. Note If the predictor is not involved in interactions or nested effects, also add the CLODDS= option in the MODEL statement.

The key to epidemiologic analysis is comparison. Occasionally you might observe an incidence rate among a population that seems high and wonder whether it is actually higher than what should be expected based on, say, the incidence rates in other communities. Or, you might observe that, among a group of case-patients in an outbreak, several report how to convert mpeg3 to mp3 eaten at a particular restaurant.

Is the restaurant just a popular one, or have more case-patients eaten there than would be expected? The way to address that concern is by comparing the observed group with another group that represents the expected level. A measure of association quantifies the relationship between exposure and disease among the two groups. Exposure is used loosely to mean not only exposure to foods, mosquitoes, a partner with a sexually transmissible disease, or a toxic waste dump, but also inherent characteristics of persons for example, age, race, sexwhat is life is beautiful festival characteristics immune statusacquired characteristics marital statusactivities occupation, leisure activitiesor conditions under which they live socioeconomic status or access to medical care.

The measures of association described in the following section compare disease occurrence among one group with disease occurrence in another group. Examples of measures of association include risk ratio relative riskrate ratio, odds ratio, and proportionate mortality ratio. A risk ratio RRalso called relative risk, compares the risk of a health event disease, injury, risk factor, or death among one group with the risk among another group.

It does so by dividing the risk incidence proportion, attack rate in group 1 by the risk incidence proportion, attack rate in group 2. The two groups are typically differentiated by such demographic factors as sex e. Often, the group of primary interest is labeled the exposed group, and the comparison group is labeled the unexposed group. A risk ratio of 1. A risk ratio greater than 1. A risk ratio less than 1. Example A: In an outbreak of tuberculosis among prison inmates in South Carolina in28 of inmates residing on the East wing of the dormitory developed tuberculosis, compared with 4 of inmates residing how to calculate p value from odds ratio the West wing.

Here is the general format and notation. In this example, the exposure is the dormitory wing and the outcome is tuberculosis illustrated in Table 3. Calculate the risk ratio. Table 3. Int J Tuberc Lung Dis ;— To calculate the risk ratio, first calculate the risk or attack rate for each group. Here are the formulas:. Thus, inmates who resided in the East wing of the dormitory were 6.

Example B: In an outbreak of varicella chickenpox in Oregon invaricella was diagnosed in 18 of vaccinated children compared with 3 of 7 unvaccinated children.

Chickenpox outbreak in a highly vaccinated school population. Pediatrics Mar; 3 Pt 1 — The risk ratio is less than 1. The risk ratio of 0. A rate ratio compares the incidence rates, person-time rates, or mortality rates of two groups.

As with the risk ratio, the two groups are typically differentiated by demographic factors or by exposure to a suspected causative agent. The rate for the group of primary interest is divided by the rate for the comparison group. The interpretation of the value of a rate ratio is similar to that of the risk ratio.

That is, a rate ratio of 1. They recorded Calculate the rate ratio. Note: Of 58 viral isolates identified from nasal cultures from passengers, most were influenza A, making this the largest summertime influenza outbreak in North America. Brit Med J ; —, — Check your answer. An odds ratio OR is another measure of association that quantifies the relationship between an exposure with two categories and health outcome.

Referring to the four cells in Table 3. Notice that the odds ratio of 5. That how to create maven plugin one of the attractive features of the odds ratio — how to install laminate wood flooring on concrete the health outcome is uncommon, the odds ratio provides a reasonable approximation of the risk ratio.

Another attractive feature is that the odds ratio can be calculated with data from a case-control study, whereas neither a risk ratio nor a rate ratio can be calculated. In a case-control study, investigators enroll a group of case-patients distributed in cells a and c of the two-by-two tableand a group of non-cases or controls distributed in cells b and d.

The odds ratio is the measure of choice in a case-control study see Lesson 1. The number of persons in the control group is usually decided by the investigator. Often, the size of the population from which the case-patients came is not known.

As a result, risks, rates, risk ratios or rate ratios cannot be calculated from the typical case-control study. However, you can calculate an odds ratio and interpret it as an approximation of the risk ratio, particularly when the disease is uncommon in the population. Calculate the odds ratio for the tuberculosis data in Table 3. Would you say that your odds ratio is an accurate approximation of the risk ratio?

Hint: The more common the disease, the further the odds ratio is from the risk ratio. Section Navigation. Facebook Twitter LinkedIn Syndicate. Section 5: Measures of Association The key to epidemiologic analysis is comparison. Risk ratio Definition of risk ratio A risk ratio RRalso called relative risk, compares the risk of a health event disease, injury, risk factor, or death among one group with the risk among another group.

Method for Calculating risk ratio The formula for risk ratio RR is: Risk of disease incidence proportion, attack rate in group of primary how to add a lock to a sliding glass door Risk of disease incidence proportion, attack rate in comparison group.

Rate for group of primary interest Rate for comparison group. Exercise 3. Using the data in Table 3. Risk ratio 5. Lesson 3 Overview. Related Links.

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Odds Ratio (OR) can be calculated manually by creating 2*2 contingency table. However, For p-value and CIs it is customary from SPSS or Epi-Info or more advanced software. You can select any level of significance you require for the confidence intervals. The odds ratio calculator will output: odds ratio, two-sided confidence interval, left-sided and right-sided confidence interval, one-sided p-value and z-score. If the test was two-sided, you need to multiple the p-value by 2 to get the two-sided p-value. Mathematically, P-value and CI show two aspects of the same thing. The 95%-CI will just scratch the tested values (i.e.: odds ratio = 1) when the P-value is , and it will include it, when.

A table of odds ratio estimates for a specific predictor, whether or not it is involved in interactions or nested effects, can also be produced by specifying the predictor in the ODDSRATIO statement.

All of these tables provide a point estimate and confidence limits for each odds ratio. If a p -value is needed instead of a confidence interval, it can be obtained in one of the following ways.

Beginning in SAS 9. Both are used in the following statements for illustration. Prior to SAS 9. A confidence interval is included if you also specify the CL option. Unlike the case of a categorical predictor, the LSMEANS statement cannot be used to provide p -values for odds ratios for continuous predictors. Instead, the following method uses the odds ratio confidence limits to determine the standard error associated with the log of the odds ratio estimate and then uses it to compute the Wald test statistic and p -value.

This method can also be used for categorical predictors regardless of their parameterization. These statements fit a model involving the interaction of the categorical Sex and continuous Age predictors. Since Treatment and Duration are not involved in interactions or nested effects, their odds ratio estimates are provided in the default "Odds Ratio Estimates" table. The following DATA step statements read the data set of saved Treatment and Duration odds ratio estimates OR and compute the standard errors of the log odds ratio estimates.

The Wald chi-square statistic and its p -value are also computed for each. The same statements are used again, changing only the data set being read by the SET statement, to compute the p -value for the SEX odds ratio. Note: In Release 9. See this Problem Note. This content is presented in an iframe, which your browser does not support.

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## 4 thoughts on “How to calculate p value from odds ratio”

1. Yozshugor

Great exercise

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