Minimum detectable effect size for main outcomes (accounting for sample
design and clustering)
Power for selection into the experiment (All treatment information is put into the invitation letters):
Based on pilot data, we expect that acceptance and participation rates in group A will be about 12%-20%. With a sample size of 4,000 invitations in group (A) versus group (B) with alpha=0.05, power=0.80, we will be powered to detect a 2.5 percentage point difference in the acceptance rate between these two groups if the acceptance rate is 20% or a 2.1 percentage point difference if the acceptance rate is 12%.
For the groups which test mechanisms (C), (D), (E) and (F), with 2000 invitations in each of these groups, for the comparisons between A vs. E, A vs. F, B vs. C, and B vs. D we will be powered with alpha=0.05, power=0.80 to detect a 3.1 percentage point difference in acceptance rates if the true acceptance rate is 20%, while we will be able to detect a 2.6 percentage point difference if the true acceptance rate is 12%.
Power for applicant level outcomes:
We base our power calculations on the binary callback (0/1) for a candidate. From pilot data we expect the callback rate to be about 10 percentage points different between our advantaged versus disadvantaged candidates when that is female vs. male (the difference will likely be larger for Black vs. White and Crime vs. NoCrime given previous audit meta-studies). Our pilot data also suggests an intra-recruiter correlation coefficient of 0.05. We simulated data for our regression of interest with stratified randomization, callback as the dependent variable and treatment and treatment x advantaged candidate variables, clustered at the strata level and including recruiter fixed effects. Based on 1000 simulations with 360 recruiters in each of treatment arms (A) and (B) we have 98.6% power to detect the 10pp change for main effect. And with 180 each in groups (C)-(F) we have 95% power to detect the 10pp change in callback rates for the mechanism comparison to (A) or (B).