Why finding the average doesn't help anybody.
When I used to lead a cruise line music department, I'd always be asked to look at average team performance as a way to measure, "how we're doing?"
Based on the fleet's average performance, we'd make different decisions that would support the operation.
There are two rules that I've learned in this work:
What can be measured gets managed - often times poorly.
Average only exists as a number - it doesn't actually exist in real life.
You can argue that the fleet's average offers you insight into how a majority of the groups might operate. And yes, that's a healthy way to consider performance. But that's like grading on the curve, we're only helping the late majority/laggards. The law of diffusion of innovation would say these teams are going to be slow to adopt change. So why make the investment?
I argue, let's prop up those sites that are making the most significant change. Something happened that made their work special. Or, why not look at the outliers - the extreme high and low performers? What are they doing that's working? How can we continue supporting their efforts?
When the outliers, the innovators, the neophiliacs, the drivers are invested in your mission, they'll pull the rest of the curve with them. When you try to push the curve from behind to catch up, you risk starving the innovators of the chance to innovate. Or, worse, you're killing their creativity.
The average only exists as a number.
And numbers don't have heartbeats.