The so-called discrepancy with the 28% mortality reduction estimated for the 1975 1991 observation period is largely explained by the difference in follow-up time.
Therefore we applied the CISNET Stanford model scaled to the observed Norwegian breast cancer mortality reduction to estimate the likely screening effects by age and time since screening.
The absolute mortality reductions are estimated from the NLST results, both directly and extrapolated to long term follow-up as described in the Materials and Methods section.
To study this issue we will start with a less costly and time-consuming approach and estimate mortality reduction through a micro-simulation model: MISCAN, a well-validated micro-simulation model, originally developed to estimate the cost-effectiveness of the population-based screening program in the Netherlands [ 38- 40].
The estimated mortality reduction in the screening program is similar to the PSE estimates because the long-duration of screening (5 annual or 3 biennial screenings followed by 3 5 years hiatus followed by 5 annual or 3 biennial screenings) in the trial approximated the 21 years of periodic screening.
28, 29 By using our estimate for mortality reduction (43%) and a compliance rate of 84%, our estimate of the mortality reduction on the population level is 36% (43% × 84%) in favor of the invited women.
Take the roughly one-quarter of the estimated mortality reduction was due to "external causes" (injuries, suicide, homicide, complications of medical treatment, and substance abuse).
After correcting for anticonservative and conservative biases, the estimated mortality reduction was 25% (odds ratio = 0.75; 95% confidence interval: 0.49, 1.14; P = 0.09).
Adjusting for self-selection bias using the more conservative intention-to-treat analysis (Duffy et al, 2002) gave a 35% estimated mortality reduction (OR=0.65, 95% CI: 0.48, 0.88; P=0.005).
Use of mammography outside the program, both among nonscreened women and in between 2 screening rounds among screened women, could have reduced the estimated mortality reduction in our study.
