An additional factor is evident from a closer look at the situation in England, which may well be relevant to other countries. While incidence, mortality and rates of carcinoma in situ were increasing in women below 35 years of age, those were the women from whom 65% of Pap smears were taken at the time (Brindle et al. 1977) whereas the overall screening coverage (age 25-64 years) in the 1980s was estimated at around 12% (Quinn et al. 1999).
It was estimated that screening coverage in the 1970s reached 80% in women below 35 years of age: thus incidence was increasing in the age groups most actively screened (Adelstein 1981).
In a review of the history of cervical screening in England, Albrow et al. (2012) refer to the screening programme in the 1970s and 1980s being disorganized with poor quality control. They describe several well-publicised screening errors that lead to greatly improved quality control in the new NHS Cervical Screening Programme (NHSCSP) launched in 1988.
Importance of quality control in controlling cervical cancer incidence when risk of disease was increasing
Quality control of all aspects of the screening programme is required, from taking the samples, screening and reporting the cytology, following up women with cytological abnormalities, and carrying out colposcopy, treatment of high-grade abnormalities and follow up after treatment (Arbyn et al. 2010).