Great set of resources available here:
For every design change you make affecting your user’s experience, do you know if you’re having a positive or negative impact? Are you adding to your organization’s bottom line or eroding it? Are you sure?
The health of the business must be the highest priority for designers. With a plethora of fast and cheap analytics tools available that bring us the ability to measure almost anything, we have no excuse not to be measuring every design change we make.