You can often tell how much research a prof does by the size of their group. If they have 2 grad students and no post docs, they're probably active in a lot of research. If they have 45 grad students and 15 post docs, they're probably sitting on committees, writing grants proposals or are travelling to conference for 99% of their time. That's not necessarily a bad thing either, there is plenty of good work done by profs in a management role.
Not the same subject area, but this is why places such as Janellia Farms [1] restrict the size of their research groups. A PI with more than 6 people under her is considered a manager rather than a researcher.
