Screening mammography participation and invitational strategy: the Quebec Breast Cancer Screening Program, 1998-2000.

In the Quebec Breast Cancer Screening Program, a personalized letter signed by a regional program physician is sent to every woman in the province 50 to 69 years of age, inviting her to have a screening mammogram. A reminder letter is also frequently sent. The aim of this study was to evaluate the influence of this screening invitational strategy on rates of participation. The population studied was comprised of 684,028 women in Quebec aged 50-69. The baseline (expected) monthly mammography screening rate was estimated from the rate of screening mammograms recorded between the date a woman became eligible for screening and the mailing date of her personalized invitational letter; the observed monthly mammography screening rate was calculated after the mailing of the letter. Compared to baseline (expected) screening rates, observed rates were substantially increased (p<.05). The ratios of observed to expected rates were respectively 3.05 and 2.23 in the second and fourth months, respectively, after the letter mailing, coinciding with the mailing of the initial and reminder letters. In the twelve months after the mailing, the ratio of observed to expected rates was 1.68 (95% CI: 1.67-1.69). Twelve months following the mailing, 30 percent of the women who were letter recipients had undergone a screening mammography, compared to an expected cumulative probability of 20 percent for women not receiving a letter. The strength of this effect was similar to one seen in randomised controlled trials.