Phi Coefficient

Problem

Return the phi coefficient for a 2x2 table: (a*d - b*c) / sqrt((a+b)(c+d)(a+c)(b+d)). Return 0.0 when any margin is zero.

Hint

Phi is the Pearson correlation between two binary variables.

case 1

in: [10,20,30,40]

expected: -0.0890870806374748

case 2

in: [10,0,0,10]

expected: 1

case 3

in: [5,5,5,5]

expected: 0

case 4

in: [1,2,3,4]

expected: -0.0890870806374748

case 5

in: [0,0,0,0]

expected: 0

Starter codePython

def phi_coefficient(a, b, c, d):
    # Your code here
    pass

5 test cases · run your code against them in the editor