What's the right size? Lab evolution

What have I done?! In a week my lab will grow to 9 people...I'm medium-sized.

— The New PI (@TheNewPI) September 2, 2015

I have taken in more part-time students in the lab few and, feeling a bit overwhelmed by this growth, I tweeted about it. This spurred a very interesting discussion about what is the "medium" size for a research lab and how much money it really takes to run a lab. This got me thinking about how much one's experience dictates how we do things in academia. As you learn to do the job of a principal investigator on the fly, you set your standards based on what you know and what you liked.

We are *well* into three simultaneous R01 awards just to cover the staff of a "medium" sized lab. No Prof effort, no supplies, reagents...

— Drug Monkey (@drugmonkeyblog) September 3, 2015

I went from being in 10-15 people labs, which were pretty much the norm where I was, to a 20+ person lab, which was not the norm, but wasn't a rare occurrence either. An average size 2 R01 lab in my experience is around 10. Not necessarily 10 fully salaried people, more 5-6 full-time and 3-4 part time students (undergrad, rotation, volunteers). When I had to think about what I wanted when I was interviewing for jobs, I decided that I didn't want a huge lab because I like mentoring and I would lose contact with my people. I liked the bustle and flow of my grad school lab, so that's what I'm going for. Also my space does not allow for more.

As you learn to be an adult by watching your parents and other adults, your experience of lab life is molded by where you grew up scientifically. I'm discovering this makes a huge difference in how you design your lab and how you adjust to different environments. In parallel, your personality and how you prefer to be treated dictate how you treat others. Learning how to leverage different personalities and how to manage people that do not think like you is one of the biggest difficulties you encounter as a leader. You may want to work with people who are highly independent and able to think on their feet, but this type of worker may get bored doing more menial tasks or very repetitive project that you still need done. I am having frequent discussions with my colleagues on how they deploy undergraduates and high-school students, and whether they prefer postdocs or graduate students. Everyone is different. Even my own thinking continues to evolve as I go along and as I balance adding more people with priorities for specific projects.  I thought I would never set up an assembly line, as there is nothing that I loathed more as a student, yet I find myself designing one because I just need things to get done. As much as I'm overwhelmed by the number of people in the lab, I'm in extreme need of them because there is just too much to do.  I'd be interested in hearing how other people deal with these issues.