You start by taking a 20-minute test, then you have a first round interview with a case which is not particularly difficult. The difficulty comes with the second-round interview, which is particularly grueling.
Before your second-round interview, you receive an email with a spreadsheet that asks you to analyze market data using excel commands, put it into graphs and also create forecasts. You then also need to read an ~11 page case, take in key insights, make recommendations on the target customer and how to position the product in a 30-minute PowerPoint presentation. You are told you won't need to spend more than 2-3 hours on it, but if you want to do a good job it will take you more than 5 hours.
The second-round interview takes 4 hours with no scheduled breaks: you can ask your interviewer to end your interview early so you have 5 minutes to get some water between interviews, but some of the interviews will run overtime and so you won't be able to.
The partners and consultants are friendly, engaging and (mostly) informal, which makes the process easier. They will drill you on your interest in healthcare consulting, however, so you should know exactly what a healthcare consulting firm does and the different areas of work they support. You should also have a good idea coming in of the areas of work you would be interested in working in and know something about them. You will also get tested with random brain teasers and thought experiments, so be ready for that. There is another case interview, which is much more complex than the first one you do and it's easy to get confused as to where it's going. The partner will put you back on track, but it's best if you can avoid needing to do that.
While I had a good relationship with the people involved throughout the process, they did not contact me to tell me that I was not selected: I had to send an email after a couple of weeks to get a reply. The person who replied to me offered to have a phone call, but did not reply when I took them up on that offer.
It's understandable that as a very small firm, Cofactor wants to make absolutely sure they have the right candidate to join their team. That being said, if you aren't in love with the company and you have other options that you're a better fit for, I would caution against going through the second round interview. It's a huge commitment, even compared to other consulting firms.