|In this case, the dimension of time flows from left
to right, suggesting that if there is any correlation
between the blue events and the red events, blue
must cause red. A straight rho (product-moment)
correlation gives an r of -.356 but when
covariance in effect shifts the blue bars to the
right there is such a high correlation that even a
jaded statistician would concede causality.
Readers will find Bradley E. Huitema's (professor
of psychology at Western Michigan University)
book Analysis of Covariance and Alternatives
(Wiley, New York, 1980) instructive. ISBN:
0471420441 : 9780471420446 -
Professor Huitema told us a new edition was
coming in January 2009. Made it in October 2011.
$125 in hardcover; $80 on Nook.