A success rate is the percentage of patients who do well after treatment. How do we know that patients are "doing well"? It depends on the treatment and the criteria doctors use to evaluate the results. If you have surgery on your Achilles tendon, for example, "success" could be defined as pain relief, ability to do daily activities, getting back to work or sports--or all of the above. It can also mean improvement in measures of muscle strength or joint movement.

Measures of success vary, even for the same kinds of treatment.  When you hear a success rate, it makes sense to ask what type of success is being measured. You may also want to know whether the success rate was for a particular group of people, such as older patients or patients with chronic pain. This will let you know whether the success rate can be applied to you.