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Welcome to the PSNAP Perpetual Problem Generator!

PSNAP is the "Psychology Student Numeracy Assistance Program". It's what I call the extra help sessions that I offer to students in the psychology program here at SMU. During the regular academic year, I get together with a bunch of of students every Friday from 2pm to 5pm and we do stats stuff. It's an informal thing, and a chance for students to practice stats and ask questions in a relaxed environment outside of the regular classroom setting. The sessions are free and open to anyone who wants to come by and get in touch with their inner stats geek. Contact me ( for more information.

The problem is that three hours a week is not enough time to practice stats if you really want to master the material. That's what this page is for. It's a stats problem generator and a sort of 'statsopedia'. Here's how it works:

  • Choose a statistic from the drop-down list at the top of the page.
  • Click the "Give me a practice problem!" button. A new problem will appear in the workspace every time you push this button.
  • Read the question, and then try to solve the problem by hand (using paper, a pencil, and a calculator).
  • Click the "SHOW ANSWERS" button to check your work.
  • If you are stuck along the way and need a little hint, many of the items listed in the workspace are "clickable". I've linked them to formulae and other useful information that will appear in this window.
A few notes on my teaching philosophy:
First, I never use computational formulae. I don't see the point. If you are looking for a fast way to compute a statistic, use a computer. If you are looking to understand what the statistics are actually doing, then learn the definitional formulae. A "definitional formula" is a formula that says exactly what it is doing when you read it out loud in English. For example, the definitional formula Σ(X - M)2 reads "Get the sum (Σ) of the squared (2)deviations of the mean (M) from the raw scores (X)". If you can read the formula, you know what math to do! No studying required!

I'm a huge fan of doing math by hand. A lot. Like... a LOT a lot. I believe that you don't truly understand something until you can do it in your sleep. That's why there are so many blanks to fill in when you work through my problem sets. I'm not a fan of giving you any arithmetic answers for free. Ideally, I want you to get so good at calculating (X - M) and (X - M)2 that you don't even think about it anymore. You just do it automatically. Why? Well, maybe I'm just a jerk. But I've also noticed that once the basic math stuff becomes automatic, students seem to have much less trouble with the more advanced philosophical stuff. But, that said, I manipulated the code so that most of your group means come out to nice even numbers, so calculating deviations shouldn't be too difficult. You'll only run into decimals when you practice the Repeated Measures ANOVA, and even then it shouldn't be too bad.

Stats are important. Even if you don't like 'em, understanding stats will get you a job. This is not a lie. Of all the courses that you take while studying psychology, Intro Stats and Advanced Stats are the courses that will make you employable, both inside the lab and outside. Not every employer cares about the hypothalamus. But they all care about numbers!

I hope this PSNAP app is useful. If you find any bugs, please feel free to drop me a line:

Steve Carroll PhD
Saint Mary's University
Faculty of Science
Department of Psychology