I applied to an analyst position on Nielsen's website and a few weeks later, HR reached out to me for a phone screen. The questions were basic - walk me through your resume, tell me why you're interested in Nielsen, are you able to relocate, etc.
From there, I went to the Nielsen office in New York to interview for the position with 4 different team members (2 senior managers, director, VP) - traditional interview style. Questions were mostly behavioral ("tell me about a time when you lead a team to success"), with a few mechanics questions thrown in ("if I'm growing revenue but losing market share, what is a possible explanation for that result?"). All interviewees, no matter what the level of position is, are also required to take a 90-minute analytical assessment. This test consists of 10 word problems and 2 case studies. In order to be considered for any client service job at Nielsen, you must pass the assessment.
The final portion of the interview process is one that I know does not apply to all client service jobs - an interview with the client. I know that my client had requested to approve all new hires, but many of my colleagues never had to go through this step, so it is definitely on a case-by-case basis. In my case, the client interview was extremely basic - basically they just wanted to make sure I was a good fit for the position.