More Stats Functions

[ds26gte]

Issue brownplt/code.pyret.org#520 filed by @schanzer

We've had a few teachers ask if Pyret supports various stats functions:

• population variance
• sample variance
• t-test (multiple kinds)
• z-test
• chi-squared test
• multiple regression

Getting these implemented as a Pyret program would be great, but implementing them as part of Pyret's stats library would be much better.

(In keeping with the other stats functions, these should all operate on lists. I'll wrap them to work with tables in the DS teachpack.)

[shriram]

Thanks, @ds26gte! Can you add some tests, please?

[schanzer]

@ds26gte awesome to see this progress! I'm still hoping we can add a z-test function as well (see checklist in the issue).

[ds26gte]

@team, the z-test seems to require, in addition to the two samples, also the population (rather than the sample) variances. Please add what you think are the right arguments for the z-test and the other functions that I've already added.

[schanzer]

@ds26gte waiting to hear back about the desired contract from one of the teachers who requested these functions, which should give me a sense for whether these are close enough to what they need that I couldn't bridge the gap in a teachpack. Will wait to hear back.

[schanzer]

@ds26gte I spoke with Nancy Pfenning today, who gave the following descriptions of what the inputs to various functions should be:

z-test: list of numbers, stddev, hypothesized mean
t-test: list of numbers, mean
2-sample t-test: 2 list of numbers (can be different size), "tail-ness" (boolean operator? >,<, ≠?)
paired t-test: 2 list of numbers (error if different size, order matters), "tail-ness" (boolean operator? >,<, ≠?)
pooled t-test: 2 lists of numbers, "tail-ness" (boolean operator? >,<, ≠?)
chi-squared: 2 lists of numbers (assumes pre-summarized data)

I think this is all inline with what you have, with the exception of the z-test. Can you double-check your implementation, and let me know why it has two lists of numbers?