Four stages: 1) online application (requires recs and transcripts, 2) informational interview, 3) Stata test, 4) in person interview with people working on the project. They can take a long time to get back to you, as the internal recruiting process is somewhat disorganized. Don't be surprised if you fill out an application then don't hear back until three months later. Most difficult part for most RAs is the Stata test, although I found it easy and finished with an hour to spare. Don't remember much about interview questions. They value quant skills and experience with experimental studies.