Accuracy Versus Precision
Statisticians make a distinction between accuracy and precision.
"Precise" means sharply defined or measured. "Accurate" means truthful
or correct. Data can be very precise, but inaccurate. It would be precise
but inaccurate to say that a meter equals 29.3748 inches. It would actually
be more accurate to say that a meter equals a little over one yard,
although that may not sound as impressive.
For example, doctors often measure their patients' weight to help
evaluate their health. But a weight value by itself is an inadequate
indicator of health. It would be inaccurate to say that everybody who
weighs less than 200 pounds is healthy and everybody who weighs more
is unhealthy. People with different heights and builds have different
optimal weights, so medical professionals must use weight-height tables
or body-mass indices to interpret the health implications of a particular
A standard medical scale can measure a person's weight within about
1 pound of accuracy. A more expensive scale provides greater precision.
However, there's little point in purchasing a super-precise scale simply
to track body weight. Knowing that you weigh exactly 168.35 pounds rather
than about 170 pounds does little to improve assessment of your health.
Weight is relatively easy to measure and understand, but focusing too
much attention on weight may distract doctors and patients from considering
the other health factors that are equally important but more difficult
to measure, such as whether you eat a balanced diet, get sufficient
exercise or have adequate safety features in your home.