Intimate Partner Violence Prevalence Estimation using Telephone Surveys: Understanding the Effect of Nonresponse Bias
Louise-Anne McNutt and
Robin Lee
From the Department of Epidemiology, School of Public Health, University at Albany, Rensselaer, NY.
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ABSTRACT
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To assess the effect of nonresponse bias in telephone prevalence studies of intimate partner violence, the authors asked women visiting a health center in Albany, New York, during 1998 about their willingness to participate in telephone surveys. Women physically victimized by a male partner were more likely than other women to say they would participate in telephone surveys (66.7% vs. 44.4%, p = 0.03). Among women severely victimized, those living with their partner were less willing to participate than those not cohabiting (45.5% vs. 91.7%, p = 0.03). Including questions about willingness to participate in telephone surveys in studies of other kinds may be a useful method of identifying nonresponse bias. Am J Epidemiol 2000;152:43841.
domestic violence; health surveys; selection bias; telephone
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INTRODUCTION
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Telephone surveys are the primary source of population prevalence estimates of intimate partner violence (1
3
). Unfortunately, nonresponse rates for telephone surveys, in general, have increased over time, potentially increasing nonresponse bias effects (4
). For intimate partner violence, the response rates for national random-digit-dial telephone surveys dropped from 84 percent in the 1985 National Family Violence Survey to 72 percent in the National Violence against Women Survey, conducted in 19951996 (1
, 5
). Nonresponse rates will likely grow with the increase of telemarketing.
Understanding differences between participants and nonparticipants is essential for interpreting estimates derived from studies. Some studies of partner violence are introduced as studies of women's health. In general, participants in health surveys tend to be healthier and younger than nonparticipants (6



11
). However, the effects of nonparticipation on estimates of intimate partner violence prevalence may be difficult to predict without a study, because such violence is associated with multiple health outcomes, poorer overall health (associated with lower participation rates), and younger age (associated with higher participation rates) (12


16
). Additionally, studies comparing participants and nonparticipants tend to focus on different populations (e.g., elderly), potentially limiting their generalizability to assessment of nonresponse bias in studies of intimate partner violence. Studies of specific exposures and diseases tend to have the highest participation rates among those directly affected by the condition (17
, 18
). If surveys are introduced as studies of relationships or violence, women who have experienced intimate partner violence may be more likely to participate. The effects of nonresponse bias in studies of intimate partner violence also may be determined by factors unique to the study of violence. For example, some victims of intimate partner violence may be endangered by discussing the abuse with an outsider, potentially making this subgroup less likely to participate in a telephone survey (13
, 19
, 20
).
The purpose of this research was to learn who may be likely to participate in telephone studies of intimate partner violence. Women participating in a clinic-based study were asked about experiences of intimate partner violence and their willingness to participate in a telephone survey if they were randomly selected.
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MATERIALS AND METHODS
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African-American women seen at an urban, primary care center in Albany, New York, were asked to participate in a women's heath study that included questions on relationships and partner violence. Approximately two thirds of the patients seen at the center have earned income below the poverty line. Women were eligible for the study if they were 18 years of age or older, were seen between February 2 and April 30, 1998, and during specified research periods, and were not accompanied by an adult or child over 3 years (for safety reasons). Of the 173 women who met the study criteria, 127 women agreed to participate and answered the intimate partner violence questions and household occupants questions on the survey (completion rate = 73 percent). Women participating in the study were given $5 gift certificates for a local supermarket to compensate them for their time. The study was approved by the Institutional Review Board of the authors' university.
The physical aggression portion of the Conflict Tactics Scale (21
) was utilized to identify women who had experienced physical violence during the previous year. This scale, described in detail elsewhere (22
), is the most widely used measure of partner violence (23
). Briefly, for each physically violent behavior it describes (e.g., being pushed, shoved, hit, kicked, threatened with a gun), the respondent identifies frequency of occurrence on a scale. A total score takes into account both the severity and the frequency of the acts. We defined physical violence as any physical act against a woman by her male partner in the previous year. Additionally, respondents reporting violence were divided into two groups based on their Conflict Tactics Scale score: level I included women with scores of 19 (e.g., pushed, shoved, or grabbed once or twice during the year), and level II included women with scores of 10 or more (e.g., being beaten multiple times). All women who reported sexual abuse (i.e., forced to have sex against their will) also reported physical violence.
After extensive questions about health and health care experiences, women were asked, "Would you take part in a telephone survey about domestic violence by a university if you were randomly selected? Why or why not?" The survey also collected demographic information, such as age, marital status, and household occupants.
Data were entered into Epi Info (24
) and managed using SAS computer software (25
, 26
). Frequencies and percentages were calculated. Because sample sizes were small, Fisher's exact test and the Freeman-Halton test (27
) (an extension of Fisher's exact test) were calculated using StatXact 3 software (28
). Narrative responses to the question "Why or why not?" were summarized by researchers blinded to the women's violence status.
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RESULTS
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Of the 127 women studied, 51 (40.2 percent) indicated that they experienced at least one physically violent act from a male partner in the prior year. Both partner violence victims and nonvictims tended to be young, single, and high school educated (table 1). About a third of all women lived with a husband or boyfriend.
Most women had a telephone (specifically, 94 percent of partner violence victims and 90 percent of nonvictims). Eighty-eight percent of violence victims and 83 percent of nonvictims answered the telephone survey question. Partner violence victims were more likely than other women (66.7 (30/45) percent vs. 44.4 (28/63) percent, p = 0.03) to say they would participate in a telephone survey. Furthermore, the majority of violence victims experiencing either level of physical violence expressed willingness to participate (table 2). The results were different for violence victims with a male intimate partner living in the household, however. Of the women experiencing greater violence (level II), 91.7 percent of those not living with a male partner said they would participate, but only 45.5 percent of those with a male partner in the home said they would answer questions on the telephone (p = 0.03).
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TABLE 2. Reported willingness to participate in a telephone survey of intimate partner violence, by level of physical violence experienced during the previous year, Albany, New York, 1998
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Reviewing the reasons stated for willingness to participate in a telephone survey revealed some predictable patterns. Approximately 55 (28/51) percent of partner violence victims and 45 (34/76) percent of nonvictims provided a narrative response. Of the responders, about 61 percent of violence victims and 41 percent of nonvictims stated they would participate to educate society, educate themselves, or directly help women being abused. Alternatively, 32 percent of partner violence victims and 56 percent of nonvictims stated they did not like telephone surveys or did not think that they could be informative. The remaining women stated they "wouldn't mind participating" with no further explanation; one response was illegible. Although no women stated that it would be unsafe to participate, 10 partner violence victims, including the woman reporting the most severe violence (Conflict Tactics Scale score = 204), did not answer the telephone survey question or did not provide a reason for nonparticipation preference.
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DISCUSSION
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This study investigated differences between potential participants and nonparticipants in population-based telephone surveys about intimate partner violence. Although the sample size was small and based on women's prediction of their willingness to participate in a telephone survey, the results offer some insight regarding potential nonresponse bias. Overall, violence victims expressed more willingness to participate in a telephone survey on intimate partner violence than did other women. This finding is consistent with studies finding that individuals with a personal interest in a study are most likely to participate (17
, 18
). Thus, if all women, regardless of their relationship status, are included in a study, the prevalence of intimate partner violence may be overestimated.
However, some national studies of intimate partner violence have restricted study eligibility to married and cohabiting women (1
). This study suggests that severely abused women's willingness to participate in telephone surveys may depend on whether the partner lives in the household. The majority of married or cohabiting women who were severely abused reported reluctance to participate in telephone surveys regarding partner violence. Although no woman stated safety concerns as the reason for nonparticipation, some abused women did not state why they would refuse to participate, and safety concerns are one plausible explanation.
This study has several limitations. First, the sample size was small and limited to African-American women. Second, it is not known if women who stated they would participate in a telephone survey would do so if called. Third, some women who are severely abused may have refused to participate in this study or have limited access to health care. Additional studies should be designed to improve on the 73 percent completion proportion found in this study.
In summary, as more people refuse to respond to population telephone surveys, attention should be focused on how participants and nonparticipants differ and on the impact of these differences on prevalence estimates. Adding questions about willingness to participate in telephone surveys to studies conducted in other settings may be one way of gaining information. This practice may be especially useful in studies of partner violence, as aggressive techniques to solicit participation may be dangerous for some women and thus unacceptable.
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ACKNOWLEDGMENTS
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This study was funded by the Preventive Health and Health Services Block Grant, New York State Department of Health, and the Center for Minority Health, School of Public Health, University at Albany.
The authors thank the staff of the Whitney M. Young, Jr., Health Center for their assistance and Drs. Colin Loftin and Bonnie Carlson for their thoughtful comments.
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NOTES
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Correspondence to Dr. Louise-Anne McNutt, Department of Epidemiology, School of Public Health, University at Albany, 1 University Place, Room 130, Rensselaer, NY 12144.
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REFERENCES
|
---|
-
Straus MA, Gelles RJ. Societal change in family violence from 1975 to 1985 as revealed by two national surveys. J Marriage Fam 1986;48:46579.[ISI]
-
Tjaden P, Thoennes N. Prevalence, incidence, and consequences of violence against women: findings from the National Violence against Women Survey. Washington, DC: National Institute of Justice and Centers for Disease Control and Prevention, 1998. (NCJ publication no. 172837).
-
Bachman R, Saltzman LE. Violence against women: estimates from the redesigned survey. Washington, DC: National Institute of Justice, 1995. (NCJ publication no. 154348).
-
Remington T. Telemarketing and declining survey response rates. J Advertising Res 1992;32:68.[ISI]
-
Tjaden P, Thoennes N. Stalking in America: findings from the National Violence against Women Survey: research in brief. Washington, DC: National Institute of Justice, 1998. (NCJ publication no. 169592).
-
Biggar RJ, Melbye M. Responses to anonymous questionnaires concerning sexual behavior: a method to examine potential biases. Am J Public Health 1992;82:150612.[Abstract]
-
Benfante R, Reed D, MacLean C, et al. Response bias in the Honolulu Heart Program. Am J Epidemiol 1989;130:1088100.[Abstract]
-
Marcus AC, Crane LA. Telephone surveys in public health research. Med Care 1986;24:97112.[ISI][Medline]
-
Gilbert GH, Duncan RP, Kulley AM, et al. Evaluation of bias and logistics in a survey of adults at increased risk for oral health decrements. J Public Health Dent 1997;57:4858.[ISI][Medline]
-
Ford ES. Characteristics of survey participants with and without a telephone: findings from the Third National Health and Nutrition Examination Survey. J Clin Epidemiol 1998;51:5560.[ISI][Medline]
-
Aneshensel C, Frerichs R, Clark V, et al. Measuring depression in the community: a comparison of telephone and personal interviews. Public Opin Q 1982;46:11021.[Abstract]
-
Brown JB, Lent B, Sas G. Identifying and treating wife abuse. J Fam Pract 1993;36:18591.[ISI][Medline]
-
Flitcraft AH. Violence, values, and gender. JAMA 1992;267:31945.[ISI][Medline]
-
McCauley J, Kern DE, Kolodner K, et al. The "battering syndrome": prevalence and clinical characteristics of domestic violence in primary care internal medicine practices. Ann Intern Med 1995;123:73746.[Abstract/Free Full Text]
-
McFarlane J, Parker B, Soeken K, et al. Assessing for abuse during pregnancyseverity and frequency of injuries and associated entry into prenatal care. JAMA 1992;267:31768.[Abstract]
-
Saunders DG, Hamberger LK, Hovey M. Indicators of woman abuse based on a chart review at a family practice center. Arch Fam Med 1993;2:53743.[Abstract]
-
Axelsson G, Rylander R. Exposure to anaesthetic gases and spontaneous abortion: response bias in a postal questionnaire study. Int J Epidemiol 1982;11:2506.[Abstract]
-
Gilbart E, Kreiger N. Improvement in cumulative response rates following implementation of a financial incentive. Am J Epidemiol 1998;148:979.[Abstract]
-
Stark E, Flitcraft A. Woman battering. In: Wallace RB, ed. Maxcy-Rosenau-Last public health and preventive medicine. 14th ed. Stamford, CT: Appleton & Lange, 1998:123155.
-
Johnson H. Rethinking survey research on violence against women. In: Dobash RE, Dobash RP, eds. Rethinking violence against women. London, UK: Sage Publications, 1998:2351.
-
Straus MA. Measuring intrafamily conflict and violence: the Conflict Tactics Scale. J Marriage Fam 1979;41:7588.[ISI]
-
Straus MA. Measuring intrafamily conflict and violence: the Conflict Tactics Scales. In: Straus MA, Gelles RJ, eds. Physical violence in American families: risk factors and adaptations to violence in 8,145 families. New Brunswick, NJ: Transaction Publishers, 1990:2947.
-
Straus MA. The Conflict Tactics Scales and its critics: an evaluation and new data on validity and reliability. In: Straus MA, Gelles RJ, eds. Physical violence in American families: risk factors and adaptations to violence in 8,145 families. New Brunswick, NJ: Transaction Publishers, 1990:4973.
-
Dean AG, Dean JA, Coulombier D, et al. Epi Info, version 6: a word-processing, database, and statistics program for public health on IBM-compatible microcomputers. Atlanta, GA: Centers for Disease Control and Prevention, 1995.
-
SAS Institute, Inc. SAS language: reference, version 6. 1st ed. Cary, NC: SAS Institute, Inc, 1990.
-
SAS Institute, Inc. SAS/STAT user's guide, version 6. 4th ed. Vols 1 and 2. Cary, NC: SAS Institute, Inc, 1989.
-
Freeman GH, Halton JH. Note on an exact treatment of contingency, goodness of fit and other problems of significance. Biometrika 1951;38:1419.[ISI]
-
CYTEL Software Corporation. StatXact 3 for Windows, statistical software for exact nonparametric inference, user manual. Cambridge, MA: CYTEL Software Corporation, 1995.
Received for publication May 20, 1999.
Accepted for publication December 16, 1999.