Log-Rank Statistic

Problem

Compute a single-time-point log-rank statistic for two groups. With N = n1 + n2, expected = d * n1 / N and variance = n1*n2*d*(N - d) / (N^2*(N - 1)), return (d1 - expected)^2 / variance.

Return 0.0 when the variance is 0.

Hint

Compare observed events in group 1 against the number expected under equal risk.

Test cases

case 1

in: [100,100,20,40]

expected: 0

case 2

in: [100,100,30,40]

expected: 12.437500000000002

case 3

in: [50,50,5,20]

expected: 6.1875

case 4

in: [10,10,0,0]

expected: 0

Starter codePython

def log_rank_statistic(n1, n2, d1, d):
    # Your code here
    pass

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