Keren - 1 month ago 16
Javascript Question

# Eloquent Javascript - correlation and coefficient

Currently I'm reading Eloquent Javascript book and at chapter 4. This topic entitled 'The lycanthrope’s log ' is very confusing to me. How important is correlation and coefficient in real world programming?

I'm trying to understand the formula used to find correlation. I've far forgotten maths since I left my high school. Could, someone who've read this book, explain to me in detail, please? Below is the picture I'm wondering about..

The formula is actually pretty straight forward. Consider the table from your question.

The table states that there were a total 90 observations

Out of all 90 observations:

1. 76 times, no pizzas or squirrel
2. 9 times, pizzas but no squirrel
3. 4 times, squirrel but no pizzas
4. 1 time, both squirrel and pizza

So we want to find out how Pizzas & Squirrels are related:

Consider the equation along with your table now,

(since squirrel is on the left)

### n11 denotes an observation where there was both squirrel but pizza (4)

Now that we know what these values are, let's plug them in to our formula -

``````correlation = (1×76 - 4×9) / √(5×85×10×80)
``````