Table 1.

Evaluation of balance of age between cases and controls after matching, overall and by age category

Age category (years)	Cases		Controls		Standardized difference*
	N	Mean (SD)	N	Mean (SD)
< 5	43	3.0 (1.3)	129	2.7 (1.2)	0.257
5–14	61	9.3 (2.5)	183	9.4 (2.5)	−0.034
15–64	49	32.3 (11.5)	147	32.2 (11.6)	0.006
65+	1	72.4†	3	71.7 (4.1)	0.053
All ages	154	15.3 (14.7)	462	15.2 (14.7)	0.006

* $\text{Standardized difference}=\left(\text{sample mean of cases}-\text{sample mean of controls}\right)/\sqrt{\left(\left[{\text{sample variance of cases}}^2+{\text{sample variance of controls}}^2\right]/2\right)}$.

† Age of the single case in this age category.