  A correlation inequality is derived from local realism and a supplementary
assumption. Unlike Clauser-Horne (CH) inequality [or Clauser-Horne-Shimony-Holt
(CHSH) inequality] which is violated by quantum mechanics by a factor of $\sqrt
2$, this inequality is violated by a factor of 1.5. Thus the magnitude of
violation of this inequality is approximately 20.7% larger than the magnitude
of violation of previous inequalities. Moreover, unlike CH (or CHSH) inequality
which requires the measurement of five detection probabilities, the present
inequality requires the measurement of only two detection probabilities. This
inequality can therefore be used to test locality more simply than CH or CHSH
inequality.
