I got a call for an interview about a week after I applied through an email.
The interview was in a very relaxing manner. I was interviewed by research directors. Most questions were based on my CV but in detailed. They were very friendly like they wanna know you as a person; why you did this and that, why Ipsos, why research. Then they asked this one question that was kinda intended to assess my analytical skill and to see how well I respond to pressure. That's pretty much it, then they gave me a chance to ask back and let me choose between the company's specialisations. Then, they passed me on to another interview with another director, So, I thought I didn't get the offer but they just were being nice.
However, I received another phone call. Again, the interview was nothing stressful. It began with simple questions, then unexpectedly, it quickly moved onto the next level. Now, It's nerve-racking because I was asked to complete a report based on statistical data and to deliver a presentation based on that analysis. Fortunately, It went well. Then, about a week later I got a call for an offer which I gladly accepted.
I think it's pretty much about your characteristics and to see how well you would fit with their teams and organisation. For me the experience was pretty amazing because it's totally different from my imagination where we all sits with our backs straight the whole time. Just be your professional self.