## P-Value Calculators and Graphers in Javascript

There are a lot of online tools out there for computing p-values and test statistics associated with common statistical distributions such as the normal or Student’s t-distributions. Unfortunately, most of them are either ad-ridden or powered by Java (and hence slow to initially load and finicky when it comes to which browsers they work with). So one of my summertime projects this year was to create a website that solves both of those problems:

The website computes p-values and test statistics in real-time via javascript (and thus does not need Java or any other plug-in). The computations themselves are fairly straightforward and are performed via the trapezoid rule. The graphic on the right is composed of a static PNG that displays the appropriate distribution. The distribution’s image is transparent under the graph and opaque above the graph, which makes it easy to display the p-value graphically – the light blue area is actually just a blue rectangle that is drawn beneath the distribution’s image.

Additionally, through the magic of PHP the tool automatically creates a URL that links to the current computation (and thus makes it much more citable). So, for example, if you want to know the T-value that corresponds to a right-tailed test with 12 degrees of freedom and a p-value of 0.1, you could simply click here.

Anyway, if you’re a nerd like me then enjoy it and of course feel free to leave any feedback/suggestions that you might have.

Kathryn’s got you interested in statistics now. WEAK.

@Matthew D. Johnston – It’s true, I now occasionally dabble in the dark arts.

Hi, there:

Your tool is great for computing cut-off t values at given df values. These can then be used to estimate sample sizes as p = 1 – beta is the power. Congrats for such a great tool!

I’m happy to refer the tool in our IRW newsletter.