Dichotomous Logistic Regression
Dichotomous Logistic Regression
Why Logistic Regression is Needed
One might try to use OLS regression with dichotomous DVs. There are several reasons why this is a bad idea:
1. The residuals cannot be normally distributed (as the OLS model assumes), since they can only take on two values for each combination of level of the IVs
2. The OLS model makes nonsensical predictions, since the DV is not continuous  e.g., it may predict that someone does something more than ‘all the time’.
A Very Quick Introduction to Logistic Regression
Logistic regression deals with these issues by transforming the DV. Rather than using the categorical responses, it uses the log of the odds ratio of being in a particular category for each combination of values of the IVs. The odds is the same as in gambling, e.g., 31 indicates that the event is three times more likely to occur than not. We take the ratio of the odds in order to allow us to consider the effect of the IVs. We then take the log of the ratio so that the final number goes from negative infinity to infinity, so that 0 indicates no effect, and so that the result is symmetric around 0, rather than 1. The log of the odds ratio is known as the logit.
Featured Posts

This is a talk that I will give at NESUG in the fall.

In statistics and research design, there are two types of study: Experiments and observational studies. Some...

Often, when reading a statistics book, you will see some variation on the phrase "independent data". Many...

Many times, researchers will categorize continuous variables. For example, birth weight of human infants is...

Regression refers to a collection of techniques for modeling one variable (the dependent variable or DV), as a...

Lately, across the statistical blogosphere, the repeating discussion of R vs. SAS has started up again. In...

A frequentist fellow named Smith Kept silent (he pleaded the fifth) When the judge inquired Re assumptions...

There are many books that teach you to use SAS or that teach you to use R. There is at least one book that...

Are you writing a dissertation? Congratulations! You've gotten through undergraduate education, graduate...

The title of this post is a quote from Herman Friedman, my favorite professor in graduate school. Herman was...

This is a talk developed by David Cassell and me, and given at NESUG and SGF and WUSS

If you are a PhD student you are probably aware that it is possible to buy a dissertation. There are lots of...