ABSTRACT
First, consider the column means of$6.72 (for the conventional program) and
$8.78 (for the new program). These suggest that, overall, the new program is supe-
rior to the conventional one. In other words, if we temporarily ignore whether sub-
jects have a high school diploma, the new program seems superior to the conven-
tional one. This difference ($8.78-$6.72 = $2.06) suggests that there is what is
called a main effect. A main effect is the result of comparing one of the ways in
which the subjects were classified while temporarily ignoring the other way in
which they were classified.
