Estimated marginal Means

How Does the Distribution of a Population Impact the Confidence Interval?

Spoiler alert, real data are seldom normally distributed.

How does the distribution influence the estimate of the population mean and the resulting confidence interval?

To figure this out, we randomly draw 100 observations 100 times from three distinct populations and plot the mean and corresponding 95% confidence interval of each sample.
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Spotlight Analysis for Interpreting Interactions

by Karen Grace-Martin Leave a Comment

Not too long ago, a client asked for help with using Spotlight Analysis to interpret an interaction in a regression model.

Spotlight Analysis? I had never heard of it.

As it turns out, it’s a (snazzy) new name for an old way of interpreting an interaction between a continuous and a categorical grouping variable in a regression model. [Read more…] about Spotlight Analysis for Interpreting Interactions

Why report estimated marginal means in SPSS GLM?

by Karen Grace-Martin 53 Comments

I recently was asked whether to report means from descriptive statistics or from the Estimated Marginal Means with SPSS GLM.

The Estimated Marginal Means in SPSS GLM tell you the mean response for each factor, adjusted for any other variables in the model. They are found in the Options button. (These are the same as the LSMeans in SAS GLM).

If all factors (aka categorical predictors) were manipulated, these factors should be independent.

Or at least they will be if you randomly assigned subjects to conditions well.

In this situation only, the estimated marginal means will be the same as the [Read more…] about Why report estimated marginal means in SPSS GLM?