Socio-demographic characteristics of study participants and their male partners are presented in Table . Participants ranged in age from 14 to 48 years (mean = 26.2). At the time of the survey, 74.1% of women had a spouse or steady male partner and the majority (69.8%) had been in their relationship for over two years. A total of 57.7% of participants were pregnant sometime during the year prior to the survey. While all women were Native American, most (59.0%) of their partners were not. A total of 62% of women were enrolled with one of two local tribes and the remainder belonged to 27 different tribes, nearly all based in Oklahoma. Likewise the 41% of partners who were Native American were primarily (69%) affiliated with two local tribes and the remainder belonged to numerous Oklahoma tribes.
Socioeconomic and demographic characteristics of Native American women participants and their male partners
Approximately 30% of women and their partners had not attained a high school degree and less than 5% were college graduates. In the year prior to the survey, 49.4% of women and 18.0% of partners were unemployed, 22.4% of families received TANF or welfare, and 42.6% of families received food stamps. The majority of employed partners worked as skilled laborers. Nearly three-quarters (73.4%) of women lived at or below the federal poverty level and 30.1% lived in severe poverty (≤ 50% of federal poverty threshold). In addition, over one-third (35.7%) of women did not have a working telephone in their home.
Over half (58.7%; 95% CI: 53.0, 64.1) of study women reported experiencing physical or sexual IPV in their lifetime and 39.1% (95% CI: 33.7, 44.8) experienced severe acts of physical partner-perpetrated violence (Table ). Common forms of severe physical assault included being kicked, bit, or hit with a fist (28.2%); being choked (21.2%); and beaten up (19.6%). Nearly one in nine women had been threatened with a knife or gun by a partner. A total of 40.1% (95% CI: 34.6, 45.8) of all women reported lifetime partner-perpetrated injuries and 31.1% reported partner-perpetrated injuries to their neck, head, or face (Table ).
Lifetime and past-year prevalence of intimate partner violence and intimate partner injury among Native American women participants
Lifetime prevalence of forced sexual activity by a partner was 12.2% (95% CI: 8.9, 16.5). Only one woman reported sexual IPV but no physical IPV; most (84%) women who were sexually assaulted by a partner also reported multiple forms of severe physical IPV. The lifetime prevalence of sexual IPV was far lower among women experiencing no (0.8%) or only minor (5.3%) physical IPV, in contrast to the sexual IPV prevalence (27.9%) among women reporting severe lifetime physical IPV.
There were 273 (88%) women who reported having a spouse or boyfriend during the previous 12 months. Thirty percent (95% CI: 24.7, 35.9) of these women reported experiencing some form of physical or sexual IPV in the past year, 15.8% (95% CI: 11.7, 20.7) reported severe physical IPV, and 16.4% (95% CI: 12.3, 21.5) reported partner-perpetrated injuries (Table ). The past-year prevalence of sexual IPV was 3.3% (95% CI: 1.6, 6.4). All women (n = 9) who reported past-year sexual IPV also reported past-year physical IPV. Among women reporting past-year physical IPV, 11.0% (95% CI: 5.5, 20.3) also reported partner-forced sexual activity.
IPV during pregnancy
Among women who were pregnant in the past year, 140 (87%) answered survey questions on IPV during pregnancy. A total of 13 (9.3%; 95% CI: 5.2, 15.7) of these women reported that their partner physically or sexually assaulted or hurt them during their pregnancy. Among the women reporting IPV during pregnancy, four (30.8%; 95% CI: 10.4, 61.1) reported that the level or amount of violence was worse than before they got pregnant.
Socioeconomic and demographic factors associated with past-year IPV in univariate analyses included participant's age being less than 32 years (PR = 1.9; 95% CI: 1.0, 3.5); being divorced or separated (PR = 2.3; 95% CI: 1.6, 3.2); having six or more persons in the household (PR = 1.6; 95% CI: 1.1, 2.3); being on public assistance (PR = 2.1; 95% CI: 1.4, 3.0); and living in extreme poverty (PR = 1.6; 95% CI: 1.1, 2.2) (Table ). Partner's education and employment were much more strongly associated with past-year IPV than were participant's education and employment (Table ). Past-year IPV prevalence was 49.4% for women with partners who had not graduated from high school compared with 20.2% for women with partners who were high school graduates (PR = 2.4; 95% CI: 1.7, 3.5). Among women with unemployed partners, 40.8% reported past-year IPV in contrast to 25.9% of women with partners who were employed or full-time students (PR = 1.6; 95% CI: 1.0, 2.4).
Associations of socioeconomic and demographic factors with past-year physical and/or sexual intimate partner violence
We also examined two status inconsistency variables (data not shown). Status inconsistency based on employment (that is, participant's employment status in relation to her partner's employment) was not significantly associated with past-year IPV (p = 0.175), but status inconsistency based on education showed a strong univariate association (p < 0.001). Past-year IPV prevalence was 25.8% (95% CI: 12.5, 44.9) for women in relationships where their education status was worse than their partner's (that is, partner was high school graduate but participant was not), 23.3% (95% CI: 17.4, 30.4) for women with education equal to their partner's, and 54.8% (95% CI: 38.8, 69.8) for women in relationships where they had graduated high school but their partner had not. However, further analyses revealed that the latter rate was statistically similar to the IPV prevalence for women in relationships where neither partner had a high school degree (41.2%; 95% CI: 25.1, 59.2), indicating that variability in past-year IPV was affected by partner's education, rather than status inconsistency.
Other factors examined in relation to past-year IPV included partner's race/ethnicity, pregnancy, and lack of a home telephone (Table ). There was some variability in past-year IPV by partner's race/ethnicity (p = 0.101). Past-year IPV rates among women with Native American (33.0%) or African American (42.9%) partners were higher than among women with White (21.4%) or Hispanic (25.0%) partners. There was no association between being pregnant in the past 12 months and past-year IPV (PR = 0.9; 95% CI: 0.6, 1.3). Likewise, there was no association between lack of a residential telephone and past-year IPV (OR = 1.1), although it should be noted that 41% of women who experienced past-year IPV did not have a home telephone.
Socioeconomic measures demonstrating significant (p < 0.05) interactions with past-year IPV are shown in Table . A strong interaction was observed between public assistance and partner's education (p = 0.007). Among women not on public assistance, the past-year IPV rate was 50.0% in women with partners who had not graduated from high school compared with 11.1% in women with partners who had at least a high school degree (OR = 8.0; 95% CI: 3.3, 19.1). In contrast, there was only a nominal association between partner's education and IPV (OR = 1.7; 95% CI: 0.8, 3.6) among public assistance recipients. Similar interactions were observed between public assistance and poverty level (p = 0.028), and between poverty level and partner's education (p = 0.035).
Interactions among socioeconomic variables and past-year physical and/or sexual intimate partner violence
The interactions among socioeconomic variables each followed a pattern suggestive of a threshold effect (Table ). By far the lowest IPV rates occurred in strata with the least dire socioeconomic conditions, whereas women who experienced one or two severe socioeconomic conditions had similarly increased IPV. For example, the IPV prevalence was 18.1% for women who lived above 50% of the federal poverty level and did not receive public assistance, whereas the IPV prevalence was 44.4% for women with similar household income but who received public assistance, 42.1% for women in severe poverty but not on public assistance, and 39.7% for women in severe poverty and on public assistance.
Because all three socioeconomic measures shown in Table each had significant two-way interactions with the other two socioeconomic variables (for example, poverty level interacted with both partner's education and public assistance), we created a socioeconomic index based on these three variables to explore a three-way interaction and to examine whether IPV prevalence increased as the number of poor socioeconomic conditions increased. Each variable (partner's education: < high school graduate (HSG) versus ≥ HSG; public assistance: yes versus no; and percent of federal poverty level: ≤ 50% versus > 50%) was coded as 0 or 1 and then added together. The IPV rates associated with scores of 0, 1, 2, and 3 were 10.1%, 37.5%, 51.9%, and 36.0%, respectively. Due to limited cell sizes and no evidence of a clear trend, scores of 1, 2, and 3 were combined for multivariate analyses. Thus, women categorized in the low socioeconomic group based on any one of the three measures were compared with those categorized in the reference group for all three socioeconomic measures. As shown in Table , 42.8% of women scoring low on the combined socioeconomic index were assaulted by a partner in the past year compared with 10.1% of women in the reference group (PR = 4.2; 95% CI: 2.3, 7.8).
We attempted to examine interactions between partner's race/ethnicity and socioeconomic conditions. There was no evidence of additive or multiplicative interactions between the combined socioeconomic index and partner's race/ethnicity, although these analyses were limited by small cell sizes.
Results of the final logistic regression model of past-year IPV are shown in Table . The combined socioeconomic index was most strongly associated with past-year IPV prevalence (OR = 5.0; 95% CI: 2.4, 10.7). Other important factors were being divorced or separated (OR = 3.9; 95% CI: 2.0, 7.5); participant's age being less than 32 years (OR = 3.2; 95% CI: 1.3, 7.6); and having six or more persons in the household (OR = 2.3; 95% CI: 1.2, 4.6). Partner's race/ethnicity, participant's education, and employment variables were not significant when added to the final model. After controlling for the combined socioeconomic index, there was no association between partner's employment and past-year IPV (adjusted OR = 1.3; 95% CI: 0.7, 2.6). Likewise, there was no increased IPV prevalence associated with African American (adjusted OR = 1.3; 95% CI: 0.5, 3.3) or Native American partners (adjusted OR = 1.4; 95% CI: 0.7, 2.8) after controlling for the combined socioeconomic index and having six or more persons in the household.