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To estimate whether home visitation beginning after child birth was associated with changes in average rates of mothers' intimate partner violence (IPV) victimization and perpetration, as well as rates of specific IPV types (physical assault, verbal abuse, sexual assault, injury) during the 3-years of program implementation and during 3-years of long-term follow-up.
Randomized controlled trial
643 families with an infant at high-risk for child maltreatment born between November 1994 and December 1995.
Home visitors provided direct services and linked families to community resources. Home visits were to initially occur weekly and to continue for at least three years.
Women's self-reports of past year IPV victimization and perpetration using the Conflict Tactics Scale. Blinded research staff conducted maternal interviews following the child's birth, and annually when children were 1–3 years and then 7–9 years old.
During program implementation, intervention mothers as compared to control mothers reported lower rates of IPV victimization (Incidence Rate Ratio [IRR], 0.86; 95% confidence interval [CI], 0.73,1.01) and significantly lower rates of perpetration (IRR, 0.83; 95% CI 0.72,0.96). Considering specific IPV types, intervention women reported significantly lower rates of physical assault victimization (IRR, 0.85; 95% CI 0.71,1.00) and perpetration (IRR, 0.82; 95% CI, 0.70,0.96). During long-term follow-up, rates of overall IPV victimization and perpetration decreased with non-significant between-group differences. Verbal abuse victimization rates (IRR, 1.14, 95% CI 0.97,1.34) may have increased among intervention mothers.
Early childhood home visitation may be a promising strategy for reducing IPV.
Intimate partner violence (IPV) prevalence is disproportionately high in families with children less than five years old.1 Both IPV victimization and childhood IPV exposure are associated with adverse health consequences.2–9 Despite growing understanding of the epidemiology and health consequences of IPV, studies testing effective interventions are limited.10, 11
IPV interventions targeting women with young children are important given the elevated risk of IPV during this period and given the health implications for victims and their children. Early childhood home visitation, which traditionally focuses on reducing child maltreatment, is one method of delivering intervention services to families. However, families targeted to receive home visiting are frequently also at high risk for IPV.12 The CDC recently conducted a systematic review examining the home visitation-family violence relationship, and concluded that there was insufficient evidence to determine if early childhood home visitation reduced IPV.13
Reduction of maternal risk factors for child maltreatment, including IPV, was one of the goals of the Hawaii Healthy Start Program (HSP) early child home visitation program. Duggan, et al. have published mixed findings about HSP's effectiveness during the child's first three years of life in decreasing maternal IPV. In these publications, the authors treated IPV as a binary variable, did not evaluate sexual violence, and did not delineate the perpetrator. These limitations ignore the complexity of IPV, and thus impair our ability to estimate the association between home visitation and IPV.
Using data collected to evaluate the Hawaii HSP, we sought to estimate over two 3-year time intervals (during program implementation and over long-term follow-up) whether home visitation beginning after the birth of a child was associated with: 1) changes in average rates of mothers' intimate partner violence (IPV) victimization and perpetration, and 2) changes in rates of specific IPV types (physical assault, verbal abuse, sexual assault, injury).
Details of the Hawaii HSP study have been published.14–22 Families were eligible if they: 1) gave birth between November 1994 and December 1995 on Oahu; 2) had an English-speaking mother; 3) were not involved with Child Protective Services; and 4) the infant was at high-risk for maltreatment. The criteria for high-risk have been described elsewhere.15, 16
Families agreeing to participate provided written informed consent. Families then were randomly assigned to: 1) HSP home visiting intervention group; 2) control group; or 3) testing control group. Group assignments were randomly allocated to study ID numbers at a central office using a table of random numbers. Study ID numbers were sequentially given to each newly enrolled family. By design, more families were randomized to the intervention group than the control groups. For the current analyses, participants in the testing control group were excluded because this group was not the primary control group, had a small sample size (n=41), and did not have the same assessment schedule as the other two groups. Differences in the distributions of baseline characteristics between the primary control group and the testing control group were minimal.
Intervention families received early childhood home visitation. The content of home visits aimed to promote child health and decrease child maltreatment by improving family functioning and reducing malleable risk factors such as IPV. Paraprofessional home visitors were expected to accomplish these goals by providing direct services and by linking families to appropriate community services such as IPV shelters/advocacy groups and mental health treatment. Direct services were to include: 1) teaching about child development; 2) role-modeling positive parenting and problem solving strategies; and 3) offering emotional support. The intervention was administered by three community agencies on Oahu. Each agency operated two program sites.
The initial home visit was expected to occur within one week of the infant's birth. All intervention families were expected to participate initially in weekly visits. Visits were to taper as families achieved greater competency. Home visits were designed to be carried out for at least three years, but it was challenging to retain families. Families participated in a mean of 13.6 visits in the first year.16 Ninety percent of families participated in home visitation when the child was 3 months, 70% participated at 6 months, 49% at 12 months, and 25% at 36 months.16
Interviews with the infant's primary caregiver, generally the biological mother, were conducted in the intervention and control groups. Trained research staff blinded to the participants' group status conducted the interviews. The baseline interview occurred following the child's birth, and follow-up interviews occurred in two time periods- annually when the child was 1 to 3 years old, and then annually when the child was 7 to 9 years old. Data collection ended in 2005.
In a small percentage of cases at each follow-up point, the child's primary caregiver was not the mother or the mother could not be located for an interview; thus, the interview was conducted with an alternate caregiver. Interviews with alternate caregivers were excluded in the current analyses.
During each interview, mothers reported their IPV victimization and perpetration over the past year using the Conflict Tactics Scale (CTS). The psychometric properties of the CTS have been well-documented.23–25 At baseline, the interview included the 38-item CTS1. All subsequent interviews used the 78-item revised CTS (CTS2) which contains the following categories of questions: verbal aggression/abuse, physical assault, sexual coercion/abuse and injury. Initial validation of the CTS2 estimated that the internal reliability coefficients for each category of questions was 0.79, 0.86, 0.87 and 0.95 respectively.25 The injury items include acts of physical assault that lead to bodily harm such as “I had a sprain, bruise, or small cut because of a fight with my partner.” Four sexual coercion questions were purposefully omitted during the interviews. Confirmatory factor analyses were run in MPlus (Version 5.21) to confirm whether the previously identified factor structure was replicated in the current sample.25
Fixed response choices for each item on the CTS scales are categorical, including: never, once, twice, 3–5 times, 6–10 times, 11–20 times, and > 20 times. For our analyses, categorical responses were converted to counts as follows:24 3–5 times was coded as 4, 6–10 as 8, 11–20 as 15, and >20 times as 25.24,27 For each woman at each interview, we created the following five rates per person-year of new victimization acts: 1) total IPV (all physical assault, sexual abuse and injury acts); 2) physical assault only; 3) sexual abuse only; and 4) injury only; and 5) verbal abuse only. The same five rates per year were created for maternal IPV perpetration for each woman at each interview.
The Mental Health Index 5-item short form measured anxiety and depressive symptoms, asking women how often in the past month they had experienced specific feelings.26 Response items are on a 6-point scale ranging from all of the time to none of the time. Responses were summed and standardized to a scale of 0–100. A cutoff of <67 defined poor mental health.27
Maternal drug use was measured as self-report of any current drug use. Problem alcohol use was defined as self-report of current alcohol use together with ≥ 2 positive responses to the four CAGE questions, a validated screener for problem alcohol use.28
For 94% of intervention women and 93% of control women who provided baseline data after randomization, our overall approach was an intention-to-treat analysis whereby women were analyzed using their initial group assignment, irrespective of their actual participation in the intervention. All regression analyses were conducted using Stata 10.1™ (StataCorp; 2007).
Summary statistics were generated for the intervention and control groups to describe maternal baseline characteristics. Group differences in baseline characteristics were tested using Pearson's chi-square tests for nominal variables and Student's t-test for continuous variables. Rates of IPV for both groups at each time point, and unadjusted incidence rate ratios (IRRs) were calculated.
Analyses were conducted to determine the extent of missingness in covariates and outcomes over time. Individual follow-up interviews were missing for two reasons: 1) attrition, i.e. mother's departure from the study; and 2) mother remained in the study through the final interview but missed earlier individual interviews. To reduce bias due to missingness and lost-to-follow-up, missing data were imputed with 20 imputations using multiple imputation by chained equations.29, 30 As per the default for multiple imputation by chained equations in Stata™, each missing variable was regressed on all other variables. We report results of regression models using imputed data.
A negative binomial regression model, which accounts for over-dispersion (variance greater than mean), for cross-sectional panel data was selected because of the skewed distribution of IPV acts.31 Repeated measures of women at multiple time points violates the independence assumption required for regression. To address this non-independence, we treated each woman's multiple measures as clustered data. Analyses of IPV acts over time within a woman suggested that there was variation, and thus a random effect was added to the model to allow a unique intercept for each participant.
Primary analyses compared total rates of IPV victimization and perpetration (in separate models) between intervention and control group women when children were 1) 1–3 years old and separately when they were 2) 7–9 years old. Additional analyses compared the rates of specific IPV types between intervention and control women during the same two time periods. All models adjusted for nonequivalence, defined as a p-value <.20, between the intervention and control groups' baseline sociodemographic characteristics including: past year alcohol use (dichotomous), maternal mental health (dichotomous), and past year employment (dichotomous). Child age (continuous) was included to model time. Because of concern that study site might be a confounder, we also adjusted for site (categorical) in all analyses. Models examining total IPV victimization and perpetration controlled for baseline IPV (continuous).
We conducted two sensitivity analyses. For all reported analyses, women with no partner were coded as no IPV. However, the first sensitivity analysis was conducted to test whether omitting women who reported no intimate partner in the past year resulted in similar findings compared to our approach of coding these women as having no IPV in the past year. Secondly, we conducted a sensitivity analysis to test whether the exclusion of outliers, i.e. women with greater than 100 IPV events at any interview, resulted in similar findings to regression models including these women.
The RCT and the current analyses were approved by the authors' institutional review boards. The RCT also was approved by the Hawaii Department of Health and the 6 recruitment hospitals.
After consenting, 270 women in the control group and 373 women in the intervention group completed the baseline interview (Figure 1). Of these 643 women, 86% in the control group and 91% in the intervention group completed the final interview when the child was 9 years old. Compared to women remaining in the study, women lost-to-follow-up were more likely to be Asian (44% versus 26%) and less likely to be Native Hawaiian (20% versus 35%). Differences in the distributions of other baseline characteristics were minimal. Comparing the 39 lost-to-follow-up control women versus the 33 lost-to-follow-up intervention women, a lower proportion of the control group were employed at baseline (44% versus 70%).
In addition to missingness from attrition, some mothers who remained in the study and completed the final interview missed earlier individual interviews. Considering the two sources of interview misssingness interviews were obtained for 89% of intervention mothers at 1 year, 86% at 2 years, 87% at 3 years, 73% at 7 years, 78% at 8 years, and 78% at 9 years. For control mothers, the proportions were 86%, 87%, 83%, 69%, 71% and 69%. Eight percent of participants had missing baseline covariate data, and ≤2% of participants had response-item missingness for the outcome.
At baseline, the average past year rates of IPV by group were as follows: 1) intervention group -- victimization: 4.2 acts (standard deviation (SD) 12.0) and perpetration: 10.5 (SD 22.0); and 2) control group – victimization: 5.7 (SD 16.1) and perpetration: 10.4 (SD 21.6). Baseline characteristics of the intervention and control groups were similar, except that a lower proportion of intervention women had problem alcohol use (40% versus 48%) and poor mental health (43% versus 50%), and a higher proportion were employed in the past year (52% versus 44%) (Table 1).
At each of the six follow-up interviews, the majority of women reported being in an intimate relationship, and the proportion of women in the intervention and control groups not in relationships was similar (all p-values >0.3).
Confirmatory factor analyses suggested a good fit (CFI=.95; RMSEA=.08) to the underlying data model generated previously for the CTS2 scale. The unadjusted average rates (number of IPV acts per one person-year) of maternal IPV victimization and perpetration at each follow-up time point by group are illustrated in Figures 2 and and3.3. The distribution of all IPV rates at all time points was skewed, with the majority of women reporting no IPV over the prior year (Table 2).
During the 3-years of program implementation, intervention group women reported lower unadjusted rates of IPV victimization (21%) and lower rates of IPV perpetration (34%) as compared to the control group women (Table 3). Adjusting for potential confounders, these findings persisted (Table 3) and the intervention group women reported lower rates of maternal IPV victimization (IRR, 0.86; 95% CI, 0.73,1.01) and significantly lower rates of maternal IPV perpetration (IRR, 0.83; 95% CI 0.72,0.96) compared to control women. Intervention group women reported consistently lower unadjusted rates of maternal victimization and perpetration across all specific IPV types compared to control women. In adjusted analyses, intervention group women showed significantly lower rates of physical assault victimization (IRR, 0.85; 95% CI 0.71, 1.00) and perpetration (IRR, 0.82; 95% CI, 0.70, 0.96).
Over long-term follow-up, the unadjusted IRRs showed a 16% decrease in overall maternal IPV victimization and a 2% decrease in maternal perpetration among intervention women compared to control women (Table 3). After adjusting for potential confounders, there were small decreases in the overall IRRs of maternal IPV victimization (IRR, 0.95; 95% CI 0.77, 1.17) and perpetration (IRR, 0.98; 95% CI 0.79, 1.22). The unadjusted IRRs for the specific types of IPV were mixed. The adjusted IRRs were lower for intervention versus control group for physical abuse, sexual abuse and injury, but were higher for verbal victimization (IRR, 1.14; 95% CI 0.97, 1.34) and perpetration (IRR, 1.14; 95% CI 0.92, 1.26).
Two sensitivity analyses were conducted. The first omitted women reporting no intimate partner in the past year and the findings were quantitatively and qualitatively similar to results in which these women were coded as no IPV. The second sensitivity analysis omitted women with >100 IPV events at any interview and also yielded similar results to modeling including these women.
When compared to a control group, participation in the Hawaii HSP was associated with significantly reduced maternal IPV perpetration for the child's first three years of life. Maternal IPV victimization also decreased during this time period. Considering specific types of IPV, maternal perpetration of and victimization from physical assault were significantly reduced among intervention women compared to control women. Sexual violence, verbal abuse and injury were not significantly associated with group assignment, though low prevalence of sexual abuse and injury may have impacted our ability to detect an association for these IPV types. Over long-term follow-up, overall rates of IPV decreased in both groups, but differences between groups were no longer statistically significant. Verbal abuse may have increased in the intervention group.
Our results first should be contrasted with Duggan, et al.'s conclusion that HSP did not reduce partner psychological abuse (odds ratio (OR) 1.05; 95% CI 0.81,1.36), physical abuse (OR 0.83; 95% CI 0.63, 1.09) or injury (OR 0.81; 95% CI 0.59, 1.10) in the three-years of program implementation.15 In those analyses, the three specific IPV types were dichotomized as present/absent. In contrast, we considered IPV as a count variable, and analyses tested for a difference in rates between groups. Significant differences in IPV may not have been detected because dichotomizing an inherently continuous/count variable leads to information loss which decreases power.32 Using rates also is preferable because the cut-point of number of IPV acts where a relationship is considered to “have IPV” is arbitrary and generally not evidence-based.
To our knowledge, this is the first RCT to describe an intervention that decreases rates of female perpetrated IPV. Published surveys cite that female perpetrated IPV is a significant public health problem.33, 34 Some argue that men's and women's violence should not be considered equivalent because of different contexts, etiologies and consequences.35 Others emphasize that all violence is detrimental, and that minor acts of female perpetrated violence increase risk of severe male perpetrated violence.36
Theoretical debates aside, reducing female perpetrated IPV likely benefits public health in general and child health specifically. IPV exposed children are at increased risk for myriad adverse health consequences; compared to peers, IPV-exposed children incur greater healthcare costs, are under-immunized, and have worse social-emotional health.6–9 Exposure to maternal IPV perpetration may pose unique threats to children's health. For example, a recent study by McDonald, et al. found that maternal IPV perpetration predicted child externalizing problems after controlling for male IPV perpetration.9
Two issues complicate interpretation of how home visiting might have influenced IPV: 1) program IPV content was minimal; and 2) few families participated in the expected number of home visits. Prior publications about HSP implementation document that home visitors frequently failed to recognize IPV, and seldom linked abused women to community resources.15 The HSP program model specified that families should initially receive weekly home visiting, and that the intervention should last at least three years. HSP home visitors struggled to maintain visit frequency and to retain families.
Despite these program limitations, two important elements of home visiting program might have contributed to the decrease in IPV: 1) the home visitor-mother relationship and 2) encouragement of self-efficacy. Mothers in the intervention group trusted their home visitor, and this relationship likely provided social support and decreased isolation.14 Mothers espoused the belief that their home visitor helped them to “set goals and make a plan for reaching them.”14 When the children were two years old, intervention mothers reported significantly greater parenting efficacy and tended to report less parenting stress14; these outcomes parallel the time-point at which we observed the greatest drop in IPV for the intervention group.
IPV interventions for abused and partner aggressive women similarly focus on promoting interpersonal relationship skills and bolstering self-efficacy.37, 38 For example, Sullivan and Bybee randomized women leaving an IPV shelter to a control group or to advocacy counseling, which included improving social support and self-efficacy. Women randomized to advocacy counseling demonstrated significant reductions in re-abuse.38
There was a general decline in overall rates of IPV over time for both groups. However, when the children were 7–9 years old, the intervention group did not report significantly lower rates of IPV victimization or perpetration than the control group. Verbal abuse may have increased for the intervention group. The decreasing rates of IPV over time for both is consistent with literature documenting that IPV prevalence is highest for young women.1, 39 Additional home visits during the child's school age years may promote further reductions in overall IPV rates, though rates of verbal abuse should be carefully monitored.
These results must be interpreted in light of important limitations. Women self-reported their own and their partner's IPV over the past 12 months; this duration of recall may be prone to error.40 Although the CTS2 has been widely validated, there is no “gold standard” from which to determine the accuracy of self-reported IPV. Intervention group women may have felt compelled to portray themselves positively, and may have under-reported IPV. However, interviews were conducted by blinded research assistants who were not involved in delivering the intervention, and intervention women commonly disclosed other equally sensitive information. Despite randomization, baseline differences existed between the groups. Although we accounted for these differences, unmeasured confounders may remain.
Our findings of an association between Hawaii HSP early childhood home visitation and decreased rates of IPV during the 3-years of program implementation are encouraging, but should be interpreted cautiously. A variety of early childhood home visitation programs serve high-risk families; each of these models differs with regard to program content, home visitor training, and frequency and duration of visits. Future research should determine whether similar decreases occur in other early childhood home visiting programs, and should investigate which elements of the program may lead to reductions.
Dr. Bair-Merritt had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Megan Bair-Merritt, MD, MSCE conceptualized and designed the analyses in the current study, participated in the analysis and interpretation of data, and drafted and critically revised the manuscript. Rusan Chen, PhD conducted statistical analyses and provided critical revision of the manuscript. He received financial compensation in his role as a statistical consultant. Jacky Jennings, PhD, MPH and Lori Burrell, MA participated in analysis decisions and interpretation of data, and provided critical revision of the manuscript for important intellectual content. Loretta Fuddy, ACSW, MPH and Elizabeth McFarlane, PhD participated in the HSP acquisition of data and provided critical revision of the manuscript for important intellectual content. Anne Duggan, ScD conceptualized and designed the HSP trial, led data acquisition, participated in analysis and interpretation of the current data, and critically revised the manuscript. Dr Duggan also obtained the funding for the conduct of the HSP trial. The parent study, evaluation of the Hawaii Healthy Start Program, was supported by the Federal Maternal and Child Health Bureau (R40 MC 00029; R40 MC 00123); the Robert Wood Johnson Foundation; the Annie E Casey Foundation; the David and Lucile Packard Foundation; the Hawaii State Department of Health; and the National Institute of Health (P30MH38725). Dr Bair-Merritt is funded in part by a Career Development Award (K23HD057180) sponsored by the National Institute of Child Health and Human Development.
Trial Registration: Clinical Trials.gov; Identifier:NCT00218751; http://www.clinicaltrials.gov/ct2/results?term=NCT00218751