Errors and discrepancies in measurement of tooth size.

A. Error. This word is used correctly with two different meanings: 1. To denote the difference between a measured value and the "true" value. Except in a few trivial cases, the "true" value is unknown and the magnitude of the error is hypothetical. 2. When a number such as (±.087) is given or implied, "error" refers to the estimated uncertainty in an experiment and is expressed in terms of such quantities as standard deviation, average deviation, probable error, or precision index. B. Discrepancy. This is the difference between two measured values of a quantity, such as the difference between two measured values of the same quantity obtained by two investigators. The word "error" is often used incorrectly to refer to such differences. C. Experimental errors. When a given measurement is repeated, the resulting values, in general, do not agree exactly. The differences between the resulting values are called "experimental errors." Also, they are sometimes called "erratic" or "accidental errors." D. Systematic or constant errors. If, on the other hand, all of the individual values are in error by the same amount, the errors are called systematic or constant errors.