All cases were linked to the screening files and classified by detection method as either screen-detected, not screen-detected but with at least one screening test, never-respondent to the screening invitation or diagnosed before the screening invitation.
This corrected estimate has been obtained assuming 65% of attendance and estimating the mortality differential through the odds ratio of never-respondent to not-yet-invited women (1.11, 95% CI: 0.87 1.40).
The odds ratio corrected for selection bias was estimated with the following formula, where p is the attendance rate and ϕ is the crude uncorrected odds ratio and Dr is the mortality differential between never-respondent and not-yet-invited women: To estimate the mortality differential Dr, the odds ratio of never-respondent to not-yet-invited women was calculated.
Diagnosed within women who never responded to their invitation – the never-respondent case division.
According to Duffy et al (2002b), the correction for selection bias brought to an estimate of the corrected odds ratio for screened to never-respondent women equal to 0.55 (95% CI: 0.36 0.85), a 45% mortality reduction, confirming the protective effect of screening for those women attending (Table 2).
Restricting the analyses to invited women, the odds ratio of screened to never-respondent women corrected for self-selection bias was 0.55 (95% CI: 0.36 0.85).
All had 4-level Likert-type response scales (always, usually, sometimes, never), and all allowed respondents to indicate that they did not know the response (these were recoded to the median response).
The odds ratio of screened to never-respondent women was 0.46 (95% CI: 0.38 0.56), a 54% mortality reduction (Table 2).
'(name respondent) never go to a hospital, no, never, you say I have headache, they take your kidneys!' You know they believe that?
It consists of 30 items presented in a six point format requiring respondents to answer "never", "only once", "several times", "monthly", "weekly" or "daily" in a twelve month period.
In total, 333 (14%) of respondents never went to school, 686 (29%) attained elementary school only, 895 (38%) attained intermediate school and another 246 (10%) attained secondary school.
