Table 2: Comparison of average PPT response to treatments over time by ANCOVA with the average of two baselines as a covariate.

Sources of variation	Degree of Freedom	Mean Square	F	sig. of F	Observed power at the 0.05 level
Within + Residual	26	243.62
Regression	1	12039.49	49.42	<0.001	1.000
Experimental group	2	2155.71	8.85	0.001	0.953

Note: The normality of every dependent variable and covariate was tested by Shapiro-Wilks test (P value >0.05). The homogeneity of variance was tested by Cochrans C and Baretlett-Box F (P value = 0.366 and 0.543 respectively)