Accuracy v. Precision

“Lawyers have to be PRECISE with their language.”

Every first year law student has undoubtedly heard this phrase about a million times. There’s a major problem with it though. The problem stems from the difference between accuracy and precision. Accuracy is the degree of veracity while precision is the degree of reproducibility. The analogy used here to explain the difference between accuracy and precision is the target comparison. In this analogy, repeated measurements are compared to arrows that are fired at a target. Accuracy describes the closeness of arrows to the bullseye at the target center. Arrows that strike closer to the bullseye are considered more accurate. The closer a system's measurements to the accepted value, the more accurate the system is considered to be.
To continue the analogy, if a large number of arrows are fired, precision would be the size of the arrow cluster. (When only one arrow is fired, precision is the size of the cluster one would expect if this were repeated many times under the same conditions.) When all arrows are grouped tightly together, the cluster is considered precise since they all struck close to the same spot, if not necessarily near the bullseye. The measurements are precise, though not necessarily accurate.

So now that we’re all clear on that difference… I invite all of you to call out the first professor you hear say that thing about lawyers and precise language. Simply ask… “professor I’m unclear on the differences between accuracy and precision, would you please explain it?” Then see what happens…