BMC Cancer 2007, 7:201 http://www.biomedcentral.com/1471-2407/7/201 ability to retain observations with partially missing data [45]. Probabilities (and corresponding 95% confidence intervals) of not having had a mammogram in the past two years are computed for each tree terminal node (rep- resented by rectangles); testing for statistically significant differences in these probabilities among groups was not conducted. In the RP analysis, screening for other cancers were the major and sometimes only identified delineator for most groups. In the case where screening for other can- cers was the only identified delineator, a separate RP anal- ysis was conducted excluding this variable in order to identify other salient characteristics influencing mam- mography screening that might better inform interven- tions. Human subjects protection Institutional review board (ethical) approval was not sought for this research as it was based on a de-identified, public-use dataset. Results Table 1 shows the numbers and relative distributions of the 1521 study subjects according to mammography use within the past two years, and sociodemographic factors. Overall, 540 (35.5%) of all Asian women aged 41 or older reported not having a mammogram in the past two years. This proportion ranged from 29% among Japanese to 48% among Koreans and differed most notably by age at interview, presence of health insurance, percent of life- time lived in the U.S., citizenship status, having a usual source of care, use of other cancer screening tests, and hav- ing women's health issues. Smaller differences in the pro- portion of mammogram users were also seen by English language proficiency (among Chinese, Koreans, and Viet- namese), income, type of health insurance, family history of cancer, and pre-existing health conditions. RP results are presented graphically (Figures 1, 2, 3, 4, 5, 6, 7) with probabilities of not having a mammogram for relevant subgroups detailed in Table 2. Among all Asian subgroups combined, the optimal RP tree was based on splits of three explanatory variables (Figure 1): 1) ever having a pap screening exam, 2) having other women's health issues, and 3) having a usual source of care. Having a pap exam was the strongest delineator. 68% of Asian women who had not received a pap exam also did not have a mammogram in the past two years (node 1). Another high-risk group (node 4) comprised 62% of women who did not have a mammogram; these were women who have had a pap exam, but have had no other women's health issues and no usual source of care. In Chinese females (Figure 2), the strongest delineator of mammography screening was having ever had a colorectal screening exam. Among Chinese women who have had a Yes 919 409 Yes Has had other women’s health issues 392/93 19% (16%, 23%) 2 981 540 Ever had pap exam No No 527 316 Has usual source of care Yes No 62/131 68% (61%, 75%) 1* 497/267 35% (32%, 38%) 3* 30/49 62% (51%, 73%) 4* * Does not meet Healthy People 2010 goal 487/234 32% (30%, 34%) Had mammogram / Has not had mammogram Probability of not having had mammogram (95% CI) 2 Terminal node number yRFeiegacruusraseinv1de opladretirt,ioCnHinIgS c2l0as0s1ification tree for Asian females 41 Recursive partitioning classification tree for Asian females 41 years and older, CHIS 2001. colorectal screening exam, 17% did not have a mammo- gram within the past two years (node 1), compared to 63% among women who did not have a colorectal exam and were non-U.S. citizens (node 2). Another high-risk group was Chinese women who did not have a colorectal exam, were U.S. citizens, and had no usual source of care (node 4). Colorectal and pap screening exams were the only two delineating variables in Japanese females (Figure 3). The 107/22 17% (11%, 24%) 1 107/57 35% (28%, 42%) 3* 246 136 Yes Ever had colorectal No screening 113 69 Has usual source of care Yes No Citizen 139 114 Citizenship status 6/12 67% (45%, 88%) 4* Non-citizen 26/45 63% (52%, 75%) 2* * Does not meet Healthy People 2010 goal 487/234 Had mammogram / Has not had mammogram 32% (30%, 34%) Probability of not having had mammogram (95% CI) 2 Terminal node number 4RF1eigcyueraserivs2eanpdarotiltdioern,inCgHcIlSas2s0ifi0c1ation tree for Chinese females Recursive partitioning classification tree for Chinese females 41 years and older, CHIS 2001. Page 6 of 12 (page number not for citation purposes)