May 26, 2018

How random is your data?

Suppose you flip a coin 100 times, and it turns up heads 70 times. Is the coin fair?

Suppose you roll a die 100 times, and it shows 30 sixes. Is the die loaded?

In statistics, the chi-square test calculates “how random” a series of numbers is. But it doesn’t simply say “yes” or “no”. Instead, it gives you a confidence interval, which sets upper and lower bounds on the likelihood that the variation in your data is due to chance. See the examples below.

There’s just one function in this module chisquare. Instead of returning the bounds on the confidence interval in a tidy little two-element array, it returns an English string. This was a deliberate design choice—many people misinterpret chi-square results, and the string helps clarify the meaning.

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