BMC Cancer 2007, 7:201 http://www.biomedcentral.com/1471-2407/7/201 Background Asians and Pacific Islanders are among the most rapidly growing racial/ethnic population groups in the United States (U.S.), with most of the growth attributable to high immigration rates from Asian and Pacific Island countries [1,2]. California is one of the main geographic targets of this immigration, such that more than one-third of all U.S. Asians and Pacific Islanders (API), or four million people, now live in California [3-7]. Growth in API groups is expected to continue over time, with a projected popu- lation of 11 million California APIs by 2025 [7]. Breast cancer consistently is the most commonly diag- nosed cancer and the second most common cause of can- cer mortality among U.S. Asians; among Filipinas, it is the most common cause of cancer mortality [8,9]. Despite overwhelming clinical evidence supporting the efficacy of mammograms for reducing breast cancer mortality [10] and the Healthy People 2010 objective to have 70% of U.S. women age 40 and older receive a mammogram at least once every two years, recent population risk factor surveys have shown that use of mammography continues to vary by racial/ethnic group [11-13]. According to the 2001 California Health Interview Survey (CHIS), Whites, African Americans, and Latinas have already met the national objective of having a mammogram in the past two years (78.1%, 78.5%, and 69.9%, respectively) but Asians (67.2%) and Native Hawaiians/other Pacific Islanders (63.4%) lag behind [13]. Like other women, Asian Americans may not follow mammography screen- ing guidelines because of practical considerations such as lack of time, money, health insurance, transportation, or having a usual source of care [14-25]; lack of encourage- ment by physicians or family [14,16,22,24-27]; and per- ceptions that mammograms are inconvenient, uncomfortable, or dangerous; or perceptions that breast cancer is not a serious illness [24,26,28]. However, socio- cultural factors more relevant to immigrant groups espe- cially those recently immigrated to the U.S., like low level of education [18,26], inability to speak English [19,25,29,30], low level of acculturation [17,18,22,24,26,27,31], and racial/ethnic or cultural dis- cordance with providers [17,32], are also associated with low mammography utilization. While prior studies have been able to identify characteris- tics associated independently with use of mammography screening, most of these studies have been conducted with convenience-based, rather than population-based, repre- sentative samples of women. Moreover, relying on stand- ard regression techniques, nearly all previous studies have identified independent effects of socioeconomic and other characteristics associated with mammography use. With these traditional techniques, it is more difficult to consider the complex interactions among multiple factors for describing important high risk groups most likely not to comply with mammography screening recommenda- tions [33]. Public health interventions would be most effective and cost efficient if applied to segments of the population most at risk. Thus, in this analysis, we applied the novel statistical method recursive partitioning (RP) to a large, population-based resource to identify clustered characteristics of Asian American women most likely not to follow mammography screening guidelines and who might benefit from targeted intervention. We conducted analyses separately for Asians as a group as well as for eth- nic subgroups, because of demonstrated heterogeneity across these subgroups in screening rates [34,35] and the proportion of early stage diagnoses (51%, 41%, and 35% stage I breast cancer among Japanese, Chinese, and Filipi- nas, respectively [36]). Methods CHIS data and study sample We used population-based data from the 2001 CHIS, a telephone survey based on a geographically stratified sam- ple, identified through random-digit-dialing (RDD) that over-sampled under-represented geographic areas and ethnic groups. The data collected by CHIS, the largest state health survey, are intended to provide health planners, policy makers, county governments, advocacy groups, and communities a detailed picture of the health and health care needs among California's diverse population [37]. The CHIS sample represents the geographic and racial/ethnic diversity of California; interviews are con- ducted in multiple languages to accommodate the state's rich racial/ethnic diversity. CHIS 2001 collected informa- tion from more than 55,000 households across California and conducted interviews in seven languages: English, Spanish, Mandarin, Cantonese, Vietnamese, Korean, and Cambodian. Among the households who completed a screening interview (59.2% of RDD sample), the response rate for the adult interview across the state was 63.7% [38] for an overall response rate of 37.7%, which was compa- rable to response rates among Asians: South Asian (39.5%), Japanese (35.3%), Korean (42.5%), and Viet- namese (35.3%); response rates for Chinese and Filipino were not available from CHIS as they were included in the larger RDD samples and not in the ethnicity-specific over- sampling efforts [39]. This analysis included women of self-reported (or CHIS- imputed) Asian ethnicities who at the time of interview, did not report a prior history of breast cancer and who were aged 41 years or older. This age cut-off for sample selection was chosen because of screening guidelines rec- ommending annual mammograms starting at age 40 [40]. Those with prior history of breast cancer were excluded (N = 39 women who reported a prior diagnosis of breast can- cer, and N = 5 women for whom this status was not ascer- Page 2 of 12 (page number not for citation purposes)