# Amos, covariances and variances: Twenty Day Blogging Challenge

I came across this really interesting post on the 20-Day Blogging Challenge for teachers. I’m not sure how likely I am to be able to finish it in January since it is already the sixth and January is a really busy month for me, but we will see.

The first prompt is “Tell about a favorite book to share or teach.Provide at least one example of a cross-curricular lesson.”

One book that I like and have been reading lately is the IBM SPSS Amos 22 User’s Guide, by James Arbuckle. Unlike most documentation, it isn’t just which statements to use when. It gives a good discussion of structural equation modeling from the very basics. (Here’s a link to a free download of the guide for Amos 21. It’s pretty much the same.) The nice thing about it is, if you have Amos installed, it comes with the data that is used in the examples so you can compare your results to the book.

For no reason, I just decide to see how close the  covariance estimates you get with Amos are to the actual covariance . I ran the correlation procedure in SPSS and requested covariances using one of the Amos example data sets. Then I ran the same analysis in Amos. The estimates were all really close but not identical to the actual values, for example, the covariance of recall1 and recall2 was 2.622 and the estimated covariance was 2.556.

As far as a cross-curricular lesson – I think this might be useful if I had a chance to discuss maximum likelihood methods versus ordinary least squares. I just finished teaching a course in biostatistics and even though we did discuss logistic regression and I had a few students use logistic regression for their analysis projects, we did not have nearly enough time to delve into it in depth. I’m teaching a data mining course in August, but it is going to be using SAS Enterprise Miner, so while the concepts in the book might apply in some instances – he covers a lot of territory –  it won’t be the same software.

As I was reading this book, though, I was thinking about the diversity of students in almost every class that I have ever taught. It would be fun to teach a course in SEM, but I know that some students are still struggling with the concept of variance. So … my decision for the day is to start this week on some short instructional videos that can supplement the limited class time that we have. I think I’m going to start with the very basics – what is variance and what is covariance.