Validity of self-reported Pap smear history in Norwegian women

Objectives To assess the validity of self-reported Papanicolau (Pap) smear history in Norwegian women and to identify characteristics that influence the validity. Methods Interview data from a sample of 16,574 Norwegian women, aged 18-45, in 2004-2005, was compared with information from the population-based cytology register. Crude validity in the self-reports with respect to ever/never having taken a Pap smear was summarized. The validity of the reported interval since lost Pop smear was assessed by a smoothed distribution of the reported interval, stratified by the registered interval. Characteristics of influence on validity were identified by logistic regression for true positives (sensitivity and positive predictive value), true negatives (specificity and negative predictive value) and for more than one year discrepancy in time since last Pap smear, between reported and registered interval. Results Overall validity was summarized by: concordance = 0.9, sensitivity = 0.97, positive predictive value = 0.92, specificity = 0.55, negative predictive value = 0.78 and report-to-records ratio = 1.51. The variance in the reported interval increased proportionally with the registered interval, and women tended to underestimate the interval (telescoping). Age and registered number of years since last Pop smear had the strongest influence on ever/never and time interval validity, respectively. Conclusions Estimated screening rates, based on self-reporting without organized screening, are biased. Telescoping leads to increased risk for developing invasive disease, because women will postpone their next Pap smear.