Table 1. Two-by-two contingency table for signal detection.

	AEFI of interest	Other AEFIs	Total
Note: "a" means number of reports containing both the vaccine of interest and the AEFI of interest; "b" means number of reports containing the vaccine of interest with AEFIs other than the AEFI of interest; "c" means number of reports containing the AEFI of interest with vaccines other than the vaccine of interest; "d" means number of reports containing AEFIs and vaccines other than the ones of interest. Abbreviation: AEFI=adverse events following immunization.
Vaccine of interest	a	b	a+b
Other vaccines	c	d	c+d
Total	a+c	b+d	N