Table 4. Two-by-two contingency table for performance evaluation.

Test	Reference standard		Total
	Positive	Negative
Note: “A” means number of vaccine-AEFI combinations listed in reference standard and detected in this study; “B” means number of vaccine-AEFI combinations not listed in reference standard but detected in this study; “C” means number of vaccine-AEFI combinations listed in reference standard but not detected in this study; “D” means number of vaccine-AEFI combinations not listed in reference standard and not detected in this study.
Positive	True positive (A)	False positive (B)	A+B
Negative	False negative (C)	True negative (D)	C+D
Total	A+C	B+D	N