Evaluating the effectiveness of cervical cancer screening invitation letters
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The purpose of this study was to evaluate the effectiveness of an invitation letter on cervical cancer screening participation among unscreened Manitoba women 30 to 69 years of age. A cluster randomized trial design was used in which unscreened women (n=31,452) were randomly assigned by the forward sortation area (FSA) of their postal code to an intervention group that was sent an invitation letter (n=17,068) or a control group that was not sent an invitation letter (n=14,384). In order to ensure access to screening, a Pap test clinic was held by a health centre in 20 of the 27 FSAs in the intervention group two to three weeks after the invitation letters were mailed. Six months after the letters were mailed, 1,010 women in the intervention group (5.92%) and 441 women in the control group (3.06%) had a Pap test. Women who were sent an invitation letter were significantly more likely to have had a Pap test in the next six months compared to women who were not sent an invitation letter (Odds Ratio (OR) = 2.05, 95% Confidence Interval (CI) 1.78-2.37, p<0.001). However, women who had a Pap test clinic in their FSA were not significantly more likely to have had a Pap test compared to women who did not have a Pap test clinic in their FSA (OR = 1.04, 95% CI 0.82-1.32, p=0.76). Using the Behavioural Model of Health Services Use as a theoretical framework, predisposing, enabling, and need factors that might influence screening participation were also included as covariables in multivariable logistic regression Generalized Estimating Equation (GEE) models. There was a significant main effect of age group (p<0.001), average household income (p=0.01), area of residence (p=0.01), residential mobility (p=0.05), and access (p=0.001). Interactions between the invitation letter and each significant variable were tested. The interaction between the invitation letter and age group remained significant (p=0.02); therefore, the effectiveness of the invitation letter was related to age. Overall, 21 women (1.45%) had a high-grade Pap test result.