Wow. Colin, are you just trying to win an argument online or are you really that flippant when it comes to firing an employee? Keep in mind that we're talking about people's livelihoods, here---it's the sort of thing that can stress people out to the point of mental breakdown, even if you're not actively threatening them.
Firstly, this isn't a job interview. If someone's been working with you for long enough that they want to discuss a salary adjustment, then shouldn't your assessment of the value that they bring to the table be more informed than looking for "red flags" on the spot?
Secondly, developers are generally not familiar with basic statistics. If it's important to your business that they be better-than-average at stats, then budget some time and money for training.
Thirdly, in the real world, we make decisions from incomplete and biased information all the time. Sometimes, those decisions turn out to be wrong, but on the whole, it still works out better than pretending that we have no information at all. If you're in management and you have access to more complete information, then the smart thing for an employee to do is to have a conversation with you. It makes no sense to fire someone for that.
I have a lot of respect for your technical work, but the management style you're describing so far sounds authoritarian and abusive. I really hope that's not how you'd actually treat your reports, in practice.