Table 7. The sensitivity, specificity, and positive predictive values of an pre-epidemic warning in infectious disease surveillance in Japan, April 1999-March 2002.

	Sensitivity	Specificity	Positive predictive value
Influenza-like illness	90.4	93.7	23.9
Chickenpox	54.2	86.1	17.7
Rubella	36.4	99.2	2.5
Measles	43.7	89.3	16.3
Mumps	25.1	91.7	20.8

The numbers in the table are expressed as percentage (%)

The above result is based on the analysis of all the weekly cases per sentinel medical institution in the public health center areas (583 areas), from the beginning of week in April 1999 till the end of week in March 2002 (157 weeks).

The sensitivity is the proportion of valid pre-warnings, in the 4 weeks before the onset of an epidemic warning.

The specificity is the proportion of weeks without a pre-epidemic warning relative to the total number of weeks, in which there was no epidemic warning nor the 4 weeks before and after epidemic warning.

The positive predictive value is the proportion of valid pre-epidemic warnings relative to the total of pre-epidemic warnings.