I was going to write about the log of odds ratios and explain logarithms. This is the very, very odd fact I have noticed in most of social science – people in doctoral programs are often thrust into statistics course for which they really don’t have the basic mathematical foundation. This is because if they…

Baby Steps to Logistic regression

Going from the phi coefficient to odds-ratios. Remember the numerator for the phi coefficient was well, the odds ratio is the same two numbers DIVIDED rather than subtracted. You might think it is four numbers, but really it is not. The first number is the product of the diagonal cells (see below). The second number…

Phi coefficients, odds ratios and the F-word

Yes, I am the F-word – a feminist. I was at a faculty meeting this weekend and one of the presenters began by saying, pointing to a colleague in the audience, “I am sure Dr. Y knows more about this than me.” Several times in her presentation on analysis of assessment data she would pause…

Completely Random

I hate SQL. This is probably completely irrational, like that guy I turned down for a date in junior high school who my mom always tells me founded a very successful company and is making piles of money. No wait, it wasn’t irrational, he always tried to copy off me in Algebra, plus he was…

SAS was good today and so was the weather

It was 85 degrees in soCal today. Just thought I would rub that in for the benefit of my former and present colleagues in the frozen north. The advantage of having a blog as opposed to doing an on-line course is that I can just randomly switch subjects, which in my office is referred to…

The future has been here for a while now

We interrupt this discussion of chi-square and other categorical data analysis for a broadcast from the future … My brain is full. After three days of Macworld I have come to a number of conclusions, which I will share with you in random order, thus sparing you the expense, inconvenience and sogginess of traveling to…

Phi coefficients, Christmas and the number 42

People like familiarity. That’s probably one reason we enjoy the holidays so much – we know all the words to Silent Night, how to carve a turkey, which of the Christmas cookies taste the best. If I am going to convince you to give up statistics with which you feel comfortable, such as chi-square and…

Chi-square, by request, and not in a few words

Recently, someone asked me if I could explain chi-square in a few words. The short answer is, “No, I am incapable of using only a few words for any purpose whatsoever. If you doubt this, ask any of my children.” What is chi-square? Chi-square is a measure of relationship between two categorical variables.  For example,…

All the little models come home to nest

Categorical data analysis used to be simple. You had two nominal variables and you did a chi-square analysis. If it was statistically significant, that was all it took to make life good. Then, logistic regression came along, with the reasonable notion that: A. Dichotomous choices such as bought a candy apple/ate tofu & bean sprouts…

Satterthwaite, variances, walruses and uteruses

Statistics applies to everything. Today I was looking up examples of the Satterthwaite alternative to the pooled variance t-test. In short, a t-test is used when one wants to answer the question, “Is the difference between these two groups greater than one would expect to find by chance?” Any time you measure two groups, whether…