# CBA Office Hours on Linear Regression

It is critical for researchers in the behavioral, health, and social sciences to have a full understanding of the linear regression model. Not only is this model important in its own right, but it serves as the foundation for more advanced statistical models, such as the multilevel model, factor analysis, structural equation modeling, generalized linear models, and many other techniques. For those seeking a first exposure to linear regression or simply looking for a refresher, we’ve launched a new series of CBA Office Hours videos that starts with the basics of the simple one-predictor model and proceeds to more advanced topics. So far, we’ve posted four episodes:

We intend to add more videos as time goes on, focusing on such topics as interpretation in the multiple regression model, the difference between hierarchical versus simultaneous regression, how to incorporate categorical predictors, and how to test, probe, and plot interactions. To view all of the videos in this series in sequence, simply click the embedded video or go to our YouTube playlist on Linear Regression. You can also follow us on social media to be updated as new videos are added on this and other topics.

## My advisor told me I should group-mean center my predictors in my multilevel model because it might “make my effects significant” but this doesn’t seem right to me. What exactly is involved in centering predictors within the multilevel model?

How to specify multilevel models to obtain within- and between-group effects through centering lower-level predictors.

## What’s the best way to determine the number of latent classes in a finite mixture analysis?

Selecting the number of classes (or components) is one of the most challenging decisions to make when fitting a finite mixture model (including latent class analysis and latent profile analysis). In this post, we talk through the conventional wisdom on class enumeration, as well as when this breaks down.

## I’m reporting within- and between-group effects in from a multilevel model, and my reviewer says I need to address “sampling error” in the group means. What does this mean, and what can I do to address this?

Why between-group effects estimating in MLMs are sometimes biased, and what to do about it

## My advisor told me to use principal components analysis to examine the structure of my items and compute scale scores, but I was taught not to use it because it is not a “true” factor analysis. Help!

We explain the difference between principal components analysis and exploratory factor analysis

## I fit a multilevel model and got the warning message “G Matrix is Non-Positive Definite.” What does this mean and what should I do about it?

Received the cryptic warning message “G matrix is non-positive definite”? Learn what this means and what to do about it.