Good graphs are extremely powerful tools for communicating quantitative information clearly and accurately. Unfortunately, many of the graphs we see today confuse, mislead, or deceive the reader. These poor graphs result from two key limitations. One is a graph designer who isn’t familiar with the principles of effective graphs. The other is software with a […]

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Multicollinearity is one of those terms in statistics that is often defined in one of two ways: 1. Very mathematical terms that make no sense — I mean, what is a linear combination anyway? 2. Completely oversimplified in order to avoid the mathematical terms — it’s a high correlation, right? So what is it really? […]

I’ve written about this before–there is just something about statistics that makes people feel…well, not so smart. This makes people v-e-r-y reluctant to ask questions. This fact really struck me years and years ago. Hit me hard.

How do you know your variables are measuring what you think they are? And how do you know they’re doing it well? A key part of answering these questions is establishing reliability and validity of the measurements that you use in your research study. But the process of establishing reliability and validity is confusing. There […]

It’s easy to think that if you just knew statistics better, data analysis wouldn’t be so hard. It’s true that more statistical knowledge is always helpful. But I’ve found that statistical knowledge is only part of the story. Another key part is developing data analysis skills. These skills apply to all analyses. It doesn’t matter […]

Multilevel models and Mixed Models are generally the same thing. In our recent webinar on the basics of mixed models, Random Intercept and Random Slope Models, we had a number of questions about terminology that I’m going to answer here. If you want to see the full recording of the webinar, get it here. It’s […]

The last, and sometimes hardest, step for running any statistical model is writing up results. As with most other steps, this one is a bit more complicated for structural equation models than it is for simpler models like linear regression. Any good statistical report includes enough information that someone else could replicate your results with […]

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.

What does it mean for two variables to be correlated? Is that the same or different than if they’re associated or related? This is the kind of question that can feel silly, but shouldn’t. It’s just a reflection of the confusing terminology used in statistics. In this case, the technical statistical term looks like, but […]

Effect size statistics are required by most journals and committees these days — for good reason. They communicate just how big the effects are in your statistical results — something p-values can’t do. But they’re only useful if you can choose the most appropriate one and if you can interpret it. This can be hard […]