Author Archives: StatsProf

What are Z-Values in Logistic Regression?

Very Short Answer The z-value is the regression coefficient divided by its standard error. It is also sometimes called the z-statistic. It is usually given in the third column of the logistic regression regression coefficient table output. Thus, in the … Continue reading
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How Big a Sample? How Many X-Variables?

In this article address how much data you need in order to run standard logistic regression analyses. As is the case in essentially all statistical analysis, the amount of data you need in logistic regression depends on the number of … Continue reading
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Understanding Logistic Regression Coefficient Output:
Part 5 — Assessing Uncertainty

This article discusses using the logistic regression coefficient table output to assess uncertainty. It is the last part of a 5-part series focused on understanding and interpreting the logistic regression coefficient table. Click here to see a brief summary of … Continue reading
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Understanding Logistic Regression Coefficient Output:
Part 4 — Making Predictions

This article discusses making predictions using logistic regression. It is part 4 of a five-part series focused on understanding and interpreting the logistic regression coefficient output table. Click here to see a brief summary of the focus of each of … Continue reading
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How to Solve the Logistic Regression Equation for the Probability p.

As discussed previously, in logistic regression the log odds is modeled as a linear function of the -variables. That is     To solve this equation for , we first apply the exponential function to both sides of the equation: … Continue reading

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Logistic Regression Odds Ratio — The Math

In this article, I am going to show you why the odds ratio for an -variable in a logistic regression is simply the exponential of the regression coefficient. This article just contains “the math” and no interpretation. A discussion of … Continue reading

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Understanding Logistic Regression Output:
Part 3 — Assessing the Effects of the X-Variables

In logistic regression, as in least-squares regression, you often want to try to assess the effects of the independent -variables on the dependent -variable. In logistic regression, however, things are somewhat more complicated than in least-squares regression as I explain … Continue reading
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What is the Odds Ratio in Logistic Regression?

Most logistic regression software outputs (or can be asked to output) odds ratios along with the regression coefficients. These odds ratios are the exponential of the corresponding regression coefficient:     For example, if the logistic regression coefficient is the … Continue reading

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Understanding Logistic Regression Output:
Part 2 — Which Variables Matter

This article discusses one of the most important uses of the coefficient table, determining which variables matter. It is the second part of a five-part series discussing the logistic regression output coefficient table and its uses. Click here to see … Continue reading
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What is the (Multivariate) Logistic Regression Equation?

In logistic regression, the log odds is modeled as a linear functions of the -variables. Thus, the logistic regression equation is:     Once the logistic regression has been “run,” the software will calculate estimates for , , , … … Continue reading

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