Most people imagine the test conducted by user experience analyst or researchers to be very qualitiative. Heavy focus on how a users is feeling and what they are thinking as they move through a process, however, there is a place for quantiative research as well. Much of it comes from "rates" gathered through the testing. Error rates, success rates, time it takes to complete a task.
These things can be very valuable relative to heuristic analysis in trying to get your application to a certain bench mark standard. Still though, there are things would be hard to gather just out of quantitative data. Like for example if many of the errors occured because the users expected the world "Start" or "Begin" instead of "Create" or vice versa. The most important thing when it comes to measuring at the end of the day is knowing that you are actually measuring the right metric to accomplish whatever you're goals are.