Among the 1765 potentially eligible women, 346 women (19.6%) provided no information about their income and were excluded, leaving a total sample of 1419 women in our study. The proportion of nonresponse to the income item observed in this study was similar to that in national surveys, such as the National Health Interview Survey (NHIS).16
Fifteen percent of the women (n
= 207) reported low income. Mammography use was lower among low-income (31.9%) compared with high-income women (48.9%). Lower-income women were older; less educated; more likely to be non-white, unemployed or retired, unmarried, living with non-relatives; and less likely to have had a prior mammogram or a recent Pap smear than high-income women (). There were many differences between lower-income and higher-income women for variables measuring attitudinal beliefs. Lower-income women were more likely to believe that having a mammogram is frightening, feel the inconvenience of getting a mammogram is unacceptable, believe that having a mammogram is unnecessary at their age, not want to know if they had cancer, and be confused by contradictory information about mammography (). There were no differences by income in attitudes reflecting anxiety about the mammogram (e.g., physical discomfort, radiation, embarrassment) or about waiting for results (data not shown). The only facilitating condition associated with income was ease in arranging transportation; there were no differences in transportation method, issues related to making an appointment, or perceived courtesy of staff (data not shown).
Twenty-eight percent of the women (n = 393) reported no previous mammogram, and these women were significantly less likely than women who had had a previous mammogram to receive a mammogram during the study period (). When stratified by past mammography behavior, mammography receipt was associated with being in one of the telephone intervention groups, higher income, younger age, employment status, and having a recent Pap test (). Women who did not get a mammogram during the study period were more likely to report negative attitudes ().
Higher-income women were more likely to get a mammogram when it was recommended, regardless of their previous screening behavior (). For women who had a previous mammogram, employment, living alone, recent Pap test, and four attitudinal or facilitating conditions (believing mammography is unnecessary at her age, whether women friends thought she should have a mammogram, knowledge of the likelihood of getting breast cancer, and ease of arranging transportation) each independently explained part of the relationship between income and mammography, with significant percent excess risks for individual mediators ranging from 13.8% (Pap smear in past 4 years) to 20.7% (employment). After accounting for all seven mediators identified in the base models in the multivariable model, there was no association between income and mammography receipt for women with a prior mammogram (HR 1.13, 95% CI 0.82–1.54), explaining 77.6% of the relationship between income and mammography.
Table 2. Hazards Ratios (HR) and 95% Confidence Intervals (CI) for Mammography Receipt within 12 Months of Invitation to Schedule a Mammogram among Higher, Income Relative to Lower-Incomea Women: Univariate Analysis, Base Modelb Mediator Analyses, and Overall (more ...)
For women with no previous mammogram, five of the seven variables described (employment, living alone, mammogram unnecessary at her age, whether women friends thought she should have a mammogram, and ease of arranging transportation) mediated the effect of income on mammography (). Other mediators included age and several attitudes (believing that mammograms are frightening, beneficial, important even without cancer signs; may detect cancer that a clinician cannot find; provider recommendation; being confused by contradictory information about mammography). Mediators appeared to have a greater impact on explaining the income-mammography receipt relationship among women with no prior mammography, with seven variable individually having excess risk values >30%; age, employment, and believing that mammography is beneficial and necessary at a given age individually accounted for >50% of the relationship. After accounting for individual mediators in our multivariable model in women with no previous mammogram, there was no relationship between income and mammography receipt (HR 0.91, 95% CI 0.41–2.00).
Our results were the same for women who had a previous mammogram with or without age adjustment and living status adjustment in the base model. The relationship between income and mammography was attenuated when age adjustment and living status adjustment were included in the base model, but the mediators identified did not change.