instrumental variables

Senior DS loops test causal reasoning beyond the randomized A/B test. What interviewers reward is naming the quasi-experimental method that fits and stating the single assumption it lives or dies on. Here is the answer for when randomization is off the table.

IV is the causal tool people name but cannot defend. The signal is spelling out the two conditions an instrument must meet, why one is testable and one is not, and what 2SLS actually estimates. Here is the answer.