| Abstract: | Lord (1959) has shown that the standard error of measurement of a test is, for all practical purposes, directly proportional to the square root of the number of items on the test. More specifically, Lord found empirically that the standard error of a test was equal to .  if the reliability of the test was computed by the Kuder-Richardson (KR) 20 formula. If the KR-21 formula was used, the standard error was equal to . . The present paper sets out to show how these relationships may be derived from the defining formulas of reliability and standard error of measurement, if certain simple assumptions about values of test statistics are made. |
