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regression coefficients

The Difference Between an Odds Ratio and a Predicted Odds

by Karen Grace-Martin Leave a Comment

When interpreting the results of a regression model, the first step is to look at the regression coefficients. Each term in the model has one. And each one describes the average difference in the value of Y for a one-unit difference in the value of the predictor variable, X, that makes up that term. It’s the effect size statistic for that term in the model. [Read more…] about The Difference Between an Odds Ratio and a Predicted Odds

Tagged With: marginal means, odds ratio, predicted odds, regression coefficients

Related Posts

  • Logistic Regression Analysis: Understanding Odds and Probability
  • Odds Ratio: Standardized or Unstandardized Effect Size?
  • The Difference Between Relative Risk and Odds Ratios
  • Effect Size Statistics in Logistic Regression

A Visual Description of Multicollinearity

by Karen Grace-Martin 2 Comments

Multicollinearity is one of those terms in statistics that is often defined in one of two ways:

1. Very mathematical terms that make no sense — I mean, what is a linear combination anyway?

2. Completely oversimplified in order to avoid the mathematical terms — it’s a high correlation, right?

So what is it really? In English?

[Read more…] about A Visual Description of Multicollinearity

Tagged With: confounding variable, correlations, linear combination, linear regression, logistic regression, Multicollinearity, predictor variable, Regression, regression coefficients, variance, Variance inflation factor

Related Posts

  • Eight Ways to Detect Multicollinearity
  • The Impact of Removing the Constant from a Regression Model: The Categorical Case
  • Centering for Multicollinearity Between Main effects and Quadratic terms
  • The Difference Between R-squared and Adjusted R-squared

Understanding Incidence Rate Ratios through the Eyes of a Two-Way Table

by Jeff Meyer 2 Comments

by Jeff Meyer

The coefficients of count model regression tables are shown in either logged form or as incidence rate ratios. Trying to explain the coefficients in logged form can be a difficult process.

Incidence rate ratios are much easier to explain. You probably didn’t realize you’ve seen incidence rate ratios before, expressed differently.

Let’s look at an example.

A school district was interested in how many children in their sixth grade classes played on organized sports teams. So they did a count and also noted the gender of the child. The results were put into a table: [Read more…] about Understanding Incidence Rate Ratios through the Eyes of a Two-Way Table

Tagged With: count model, incidence rate ratio, regression coefficients, two-way table

Related Posts

  • The Importance of Including an Exposure Variable in Count Models
  • Member Training: Count Models
  • Count Models: Understanding the Log Link Function
  • Poisson or Negative Binomial? Using Count Model Diagnostics to Select a Model

Missing Data Diagnosis in Stata: Investigating Missing Data in Regression Models

by Jeff Meyer Leave a Comment

by Jeff Meyer

In the last post, we examined how to use the same sample when running a set of regression models with different predictors.

Adding a predictor with missing data causes cases that had been included in previous models to be dropped from the new model.

Using different samples in different models can lead to very different conclusions when interpreting results.

Let’s look at how to investigate the effect of the missing data on the regression models in Stata.

The coefficient for the variable “frequent religious attendance” was negative 58 in model 3 and then rose to a positive 6 in model 4 when income was included. Results [Read more…] about Missing Data Diagnosis in Stata: Investigating Missing Data in Regression Models

Tagged With: dummy variable, Linear Regression Model, Missing Data, regression coefficients, Stata

Related Posts

  • Linear Regression in Stata: Missing Data and the Stories it Might Tell
  • Multiple Imputation for Missing Data: Indicator Variables versus Categorical Variables
  • EM Imputation and Missing Data: Is Mean Imputation Really so Terrible?
  • Multiple Imputation in a Nutshell

Member Training: Count Models

by Karen Grace-Martin Leave a Comment

Count variables are common dependent variables in many fields. For example:

  • Number of diseased trees
  • Number of salamander eggs that hatch
  • Number of crimes committed in a neighborhood

Although they are numerical and look like they should work in linear models, they often don’t.

Not only are they discrete instead of continuous (you can’t have 7.2 eggs hatching!), they can’t go below 0. And since 0 is often the most common value, they’re often highly skewed — so skewed, in fact, that transformations don’t work.

There are, however, generalized linear models that work well for count data. They take into account the specific issues inherent in count data. They should be accessible to anyone who is familiar with linear or logistic regression.

In this webinar, we’ll discuss the different model options for count data, including how to figure out which one works best. We’ll go into detail about how the models are set up, some key statistics, and how to interpret parameter estimates.


Note: This training is an exclusive benefit to members of the Statistically Speaking Membership Program and part of the Stat’s Amore Trainings Series. Each Stat’s Amore Training is approximately 90 minutes long.

Not a Member? Join!

About the Instructor

Karen Grace-Martin helps statistics practitioners gain an intuitive understanding of how statistics is applied to real data in research studies.

She has guided and trained researchers through their statistical analysis for over 15 years as a statistical consultant at Cornell University and through The Analysis Factor. She has master’s degrees in both applied statistics and social psychology and is an expert in SPSS and SAS.

Not a Member Yet?

It’s never too early to set yourself up for successful analysis with support and training from expert statisticians. Just head over and sign up for Statistically Speaking. You'll get access to this training webinar, 100+ other stats trainings, a pathway to work through the trainings that you need — plus the expert guidance you need to build statistical skill with live Q&A sessions and an ask-a-mentor forum.

Tagged With: Count data, count model, hurdle model, incidence rate ratio, log link, Negative Binomial Regression, Poisson Regression, regression coefficients, Zero Inflated

Related Posts

  • Poisson Regression Analysis for Count Data
  • The Importance of Including an Exposure Variable in Count Models
  • Count Models: Understanding the Log Link Function
  • When to Use Logistic Regression for Percentages and Counts

Confusing Statistical Terms #2: Alpha and Beta

by Karen Grace-Martin 28 Comments

Oh so many years ago I had my first insight into just how ridiculously confusing all the statistical terminology can be for novices.

I was TAing a two-semester applied statistics class for graduate students in biology.  It started with basic hypothesis testing and went on through to multiple regression.

It was a cross-listed class, meaning there were a handful of courageous (or masochistic) undergrads in the class, and they were having trouble keeping [Read more…] about Confusing Statistical Terms #2: Alpha and Beta

Tagged With: alpha, beta, Intercept, regression coefficients, type II error

Related Posts

  • Series on Confusing Statistical Terms
  • Interpreting Regression Coefficients
  • What’s in a Name? Moderation and Interaction, Independent and Predictor Variables
  • How to Get Standardized Regression Coefficients When Your Software Doesn’t Want To Give Them To You

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Poisson and Negative Binomial Regression Models for Count Data

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