Table 3.
Effect | d.f. | SS | F | P-value |
---|---|---|---|---|
Drug | 2 | 0.938 | 15.40 | <0.0001* |
Psychostimulant vs. vehicle | 1 | 0.747 | 24.52 | <0.0001* |
Amphetamine vs. cocaine | 1 | 0.186 | 6.10 | <0.01* |
Time | 3 | 0.248 | 2.72 | <0.05* |
Time bin 1 vs. time bins 2, 3, and 4 | 1 | 0.087 | 2.86 | <0.05* |
Time bin 2 vs. time bins 3 and 4 | 1 | 0.073 | 2.41 | =0.062 |
Time bin 3 vs. time bin 4 | 1 | 0.091 | 2.98 | <0.05* |
Drug × time interaction | 6 | 0.178 | 0.97 | =0.445 |
Time bin 1—psychostimulant vs. vehicle | 1 | 0.100 | 3.29 | =0.036 |
Time bin 2—psychostimulant vs. vehicle | 1 | 0.055 | 1.80 | =0.091 |
Time bin 3—psychostimulant vs. vehicle | 1 | 0.315 | 10.35 | <0.001* |
Time bin 3—amphetamine vs. cocaine | 1 | 0.053 | 1.74 | =0.094 |
Time bin 4—psychostimulant vs. vehicle | 1 | 0.378 | 12.42 | <0.001* |
Time bin 4—amphetamine vs. cocaine | 1 | 0.174 | 5.73 | <0.01* |
A series of orthogonal contrasts were carried out as planned comparisons for each factor. Such tests do not inflate type I error, as the variance components (sums of squares, SS) and degrees of freedom (d.f.) are independent and additive. The SS for the interaction factor did not meet the requirement of additivity and thus the Bonferroni step-down procedure was used to maintain type I error at a constant rate. Asterisks indicate P-values that were statistically significant at an experiment-wise α of P = 0.05.