Table 6.

Regression analysis on post-vaccination log titre, by pre-vaccination log titre, augmented number of vaccinations, and age group.^{^}

Variables included	Estimates of regression model
	A (y-intercept)	3.696^*
Pre-titre	B_pre	0.630^*
Augmented number	B_NVaug	−0.448^*
of vaccinations	B_age	−0.014
Age group		(P=0.893)
	R²	0.390

^{^}

Notice that the coefficient on age group becomes insignificant when the augmented number of previous vaccinations is included.

P<0.001.