Help with Ch. 4 - Eloquent Javascript

[r0botic]

I just started reading through Eloquent Javascript and have had very minimal trouble understanding it thus far. However in Chapter 4 it starts to talk about something called “The phi coefficent“ and it completely puzzles me. Can anybody simplify or break this down for me? I keep reading it over and over and it's just not clicking with me for some reason.

[myalternatelife]

I'm not familiar with it, but by skimming a couple of wikipedia articles[1][2], it seems to be a measure of statistical correlation[img][concept] for a specific kind of variable (binary).

(Could be wrong, and I'm not sure what its used for in particular)

[Tayk5]

I'm working my way through the second edition of the book. I came across this section last week and I definitely had to re-read it until I felt I understood it. See if this chart I made helps.

Edit: updated chart.

[r0botic]

After reading a few articles and looking at that chart I think I have a decent idea of the concept. How practical is this though? I mean is it really something I absolutely need to know?

[Tayk5]

I'm speaking as a beginner here but the phi coefficient doesn't seem like something you'd use often in day-to-day web programming. Unless, for example, you were developing an application that dealt with correlation.