Larger Optic Nerve Heads Have More Nerve Fibers in Normal Monkey Eyes

Abstract

<h3>To the Editor.</h3> —We would like to draw attention to the statistical interpretation of data represented by Quigley et al¹in the October 1991 issue of theArchives. In Fig 1, the relationship between optic nerve fibers and optic disc is plotted with a linear regression correlation coefficient (<i>r</i>=.47,<i>P</i>&lt;.05). On examination of the plot, these data seem to have a poor linear fit and, in fact, the<i>r</i>value of.47 confirms this observation. If<i>r</i>=1, there is a perfect linear relationship and all the points lie on a straight line. If<i>r</i>=0, there is no linear relationship. Even though the correlation coefficient is greater than zero and is significant, this does not imply a good linear relationship. The real strength of a linear relationship is best indicated by<i>R</i>², which is a measure of the proportion of variation accounted for in the linear regression.