=+13.63 A sample of n 5 61 penguin burrows was selected, and values of both y 5 trail length (m) and x 5 soil hardness (force required to penetrate the substrate to a depth of 12 cm with a certain gauge, in kg) were determined for each one (“Effects of Substrate on the Distribution of Magellanic Penguin Burrows,” The Auk [1991]: 923–933).

The equation of the least-squares line was 5 11.607 2 1.4187x, and r 2 5 .386.

yˆ

x sa1b1102 sa1b1112 sa1b1102