ANOVA with One Within-subject Variable (3 of 4)
The formulas for degrees of freedom are summarized below:
df Subjects = N - 1
= 4 - 1 = 3
df Conditions = a - 1 = 2 - 1 = 1
df error = (N -1)(a-1) = 3
df total = aN - 1 = 2 x 4 -1 = 8-1 = 7
a is the number of conditions; N is the total number of subjects.
Error as Interaction
The error term in within-subject ANOVA designs is equal to the
Subjects x Condition
interaction. As
such, it is a measure of the degree to which the effect of conditions
is different for different subjects. Remember that when variables
interact, the effect of one variable differs depending on the level
of another variable. The error term is a measure of the degree to
which the effect of the variable "Condition" is different for
different levels of the variable "Subjects." (Each subject is a
different level of the variable "Subjects.") Low interaction (low
error) means that the effect of conditions is consistent across
subjects. High interaction (high error) means that the effect of
conditions is not consistent across "subjects."