IV First Stage Coefficients

Problem

Fit the first stage of instrumental variables by OLS of the endogenous regressor x on the instrument z with an intercept.

Return [intercept, slope]; if z is constant return [mean(x), 0.0], and empty input returns [0.0, 0.0].

Hint

The instrument must move the endogenous regressor for 2SLS to work.

case 1

in: [[1,2,3,4],[2,4,6,8]]

expected: [0,2]

case 2

in: [[1,2,3],[3,5,4]]

expected: [3,0.5]

case 3

in: [[2,2,2],[1,2,3]]

expected: [2,0]

case 4

in: [[],[]]

expected: [0,0]

Starter codePython

def iv_first_stage(z, x):
    # Returns [intercept, slope]
    # Your code here
    pass

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