Table 1.

Definitions of time zero and exposure status used to estimate time to SIL/CIN in Kaplan-Meier and Cox analysis

Incident HPV infection?	Lesion event?	Analysis layout* used in Tables 2 and 3	Definition of time zero	Definition of HPV exposure
No	No	1	Screening visit^†	Negative
No	No			2	Screening visit	Negative
Yes	No	1	Visit of incident HPV	By HPV type at time zero
Yes	No			2	Screening visit	HPV positivity at the last visit
No	Yes and HPV−	1	Screening visit	Negative
No	Yes and HPV−			2	Screening visit	Negative
Yes	Yes and HPV−^‡	1	Visit of incident HPV	Type at incident HPV event
Yes	Yes and HPV−^‡			2	Screening visit	Negative
Yes	Yes and HPV+	1	Visit of incident HPV	Type at incident HPV event
Yes	Yes and HPV+			2	Screening visit	Type found at incident lesion

↵* Corresponds to upper and lower sets of analyses shown in Tables 2 and 3.
↵† Preenrollment visit when subject's status was ascertained as being (a) cytologically negative, (b) seronegative for HPV 16 and HPV 18 antibodies by ELISA, and (c) HPV DNA negative by a PCR assay for 14 HR-HPV types (16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, and 68).
↵‡ HPV cleared before the occurrence of lesion.