1 Department of Epidemiology and Social Medicine, University of Aarhus, Aarhus, Denmark.
2 Department of Obstetrics and Gynaecology, Aarhus University Hospital, Aarhus, Denmark.
3 Department of Biostatistics, University of Aarhus, Aarhus, Denmark.
Received for publication August 4, 2003; accepted for publication November 3, 2003.
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ABSTRACT |
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alcohol drinking; bias (epidemiology); interviews; pregnancy; questionnaires
Abbreviations: Abbreviations: I, interview; Q, questionnaire.
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INTRODUCTION |
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It has been suggested that most of these results might be explained by the fact that the information on binge drinking used may not have covered the main period of susceptibility (9). It was therefore suggested (9) that, in order to obtain valid results, future research into the adverse effects of binge drinking during pregnancy should take into account the time of binge drinking. A method consisting of two questions asking about the number of binge episodes and the specific weeks when these episodes took place was suggested (9). From the overall distribution of data, it was concluded that no major differences were found between interviews and questionnaires (9).
The method of asking about binge drinking is being used in several cohort studies, including the Danish National Birth Cohort, which now includes 100,000 pregnancies (10). This information on binge drinking may provide useful information about the importance of timing, provided that the week-by-week information is precise. Unfortunately, the previous study on methodology did not provide information on either week-to-week variation between interviews and questionnaires or whether the women were in fact able to recall precisely during which weeks their binge episodes took place.
In Denmark, a large proportion of pregnant women admit to episodes of binge drinking (9, 11). In this study among a representative sample of 1,311 pregnant Danish women, the week-by-week agreement between two measures of binge drinking during early pregnancy obtained from interviews and questionnaires is assessed. By using two different definitions of binge drinking, we are also able to report on the internal consistency of the womens recall of binge episodes.
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MATERIALS AND METHODS |
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The Midwife Center in Aarhus is associated with the Department of Obstetrics and Gynaecology, Aarhus University Hospital. All Danish-speaking pregnant women attending routine antenatal care at the Department have been invited to fill in a self-administered questionnaire on maternal characteristics, lifestyle factors, and obstetric history when booking for delivery at the end of the first trimester.
In this study, we included all women who agreed to be interviewed and who returned the questionnaire.
Data collection
In the interview (I) and the questionnaire (Q), the women were asked identical questions on binge drinking. First, questions were asked about binge drinking defined as intake of five or more drinks on a single occasion (I5 and Q5, respectively), which is the most commonly used definition (9): "Try to think of your entire pregnancy, including the first weeks before you knew you were pregnant. How many times have you been drinking 5 or more drinks on a single occasion?" followed by: "How many weeks pregnant were you on this/these occasion(s)? Week 1 starts on the first day of your last menstrual cycle" (9). The questions were subsequently repeated, asking about intake of three or more drinks on a single occasion (I3 and Q3), which has been suggested as an alternative definition (12) based on the assumption that pregnant women and their fetuses are potentially more vulnerable to lesser amounts of alcohol. Using two different definitions made it possible to look at the consistency of the answers provided, respectively, in the interview and the questionnaire. In the interview, the I5 and I3 questions were separated by 40 other questions about alcohol intake, attitudes, knowledge, and information about alcohol. In the questionnaire, Q5 and Q3 questions were separated by three questions on the partners alcohol intake.
Our definition of a drink complied with the definition from the Danish National Board of Health; that is, one drink contains 12 g or 15 ml of pure alcohol. For the participants, the median gestational age when filling in the questionnaire was 11.1 weeks (10/90 percentiles = 7.9/18.4 weeks), and at the time of interview it was 16.1 weeks (10/90 percentiles = 13.9/21.7 weeks).
The gestational age when filling in the questionnaire and at interview was calculated in weeks from the last menstrual period adjusted for cycle length, and for women without valid information on the last menstrual period it was based on the best available clinical judgment at the time of the interview. These estimates were used because they were the ones available when the information was obtained and, therefore, the estimates referred to by the women when trying to recall their binge episodes (9).
The study was approved by the regional ethics committee and by the Danish Data Protection Agency. All women gave written informed consent.
Statistics
The agreement between the two methods was assessed by percent agreement, predictive values, and kappa (13). Bias was calculated as {[Yes (I), No (Q)] [Yes (Q), No (I)]}/N. Statistics were calculated only for women with valid information (those who answered yes or no in both the interview and the questionnaire). The possible influence of the differences in time between filling in the questionnaire and the interview on agreement, bias, and predictive values was evaluated by logistic regressions including the time gap as a continuous, explanatory variable. For all analyses, women contributed information on binge drinking only for gestational weeks for which information was available from both the questionnaire and the interview. STATA version 7 software (Stata Corporation, Inc., College Station, Texas) was used for data analysis.
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RESULTS |
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Information about five or more drinks on a single occasion
When interviewed, only 0.2 percent did not remember whether or not they had been drinking five or more drinks on a single occasion, while 3.7 percent did not remember when answering the questionnaire. There was a general tendency toward reporting more binge episodes in interviews compared with questionnaires, as illustrated with data from week 1 (table 1). Although the agreement appeared acceptable, kappa and predictive values were generally low (table 1). This tendency was the same when considering weeks 220, with agreement ranging from 82 to 100 percent, bias from 0.6 to 4.8 percent, kappa from 0.01 to 0.57, and predictive values from 0 to 67 percent (detailed week-by-week analyses may be obtained from the authors).
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Information about three or more drinks on a single occasion
When interviewed, 1.2 percent did not remember whether or not they had been drinking three or more drinks on a single occasion, while 6.0 percent did not remember when answering the questionnaire (table 1). The findings for three or more drinks were comparable with those described for five or more drinks: a higher proportion of women reporting binge episodes when interviewed than when answering the questionnaire (table 1). For weeks 220, agreement ranged from 76 to 99 percent, bias from 0.6 to 8.0 percent, kappa from 0.03 to 0.43, and predictive values from 0 to 100 percent.
Internal consistency of the interview and the questionnaire
In the interview, 0.5 percent (7/1,311) gave inconsistent information concerning the first week, while in the questionnaire, 2.8 percent (34/1,209) gave inconsistent information concerning the first week (table 3). The inconsistencies were not explained by errors in the data entry process. The data (not shown) for weeks 220 showed comparable findings. When combining data from the first 5 weeks on the women who remembered whether or not they had had binge episodes, we found that only two women gave inconsistent information in the interview, while 40 women gave inconsistent information in the questionnaire (data not shown).
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Taking into account the variation in time between filling in the questionnaire and the interview, the agreement and predictive values did not differ substantially or significantly with time, whereas bias tended to increase with an increasing time gap (p = 0.019).
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DISCUSSION |
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In this study, we found that, among women who volunteered to be interviewed and to fill in a self-administered questionnaire, all women answered the questions in the interview, and nearly all women were able to provide information on binge drinking irrespective of the definition (99.8 percent and 98.8 percent, respectively). In self-administered questionnaires, only 88.5 percent provided information on five or more drinks on a single occasion (7.8 percent did not answer the Q5 questions at all), and 79.6 percent provided information on three or more drinks (14.4 percent did not answer the Q3 questions).
This is a substantial difference, and it may be due to the womens making a special effort to remember previous binge episodes when confronted with an interviewer. The interviewers reported that many women spontaneously took out their personal diaries (not part of the study) to check when binge episodes might have occurred, and only very few women appeared uncertain of the accuracy of the information given. It is likely that many women are not as meticulous when filling in a self-administered questionnaire.
This conclusion is supported by the analyses of internal consistency: Although the binge questions in the interview were separated by 40 other questions, hardly any inconsistencies between the I5 and I3 questions were seen. In the questionnaire, the women had to turn only one page to avoid inconsistencies, and yet more inconsistencies were seen.
When women were asked questions on the same issue with a few weeks interval, it is possible that they became more aware of their drinking behavior and, when one method was consistently administered before the other, this might affect the intake reported. If so, one would expect the women to report a lower intake at the second point in time. Yet, the women reported more binge episodes in the interviews compared with the questionnaires.
Traditional wisdom says that self-administered questionnaires may yield higher estimates of alcohol intake compared with interviews, because a self-administered questionnaire requires no verbal or nonverbal justification for the answers given, whereas information from interviews might tend to cluster around socially acceptable norms because of an interviewer effect (14). Two previous studies comparing prospective information on alcohol intake in pregnancy obtained from questionnaires and interviews have failed to confirm these suggestions (14, 15).
Altogether, the agreement between the information from interviews and self-administered questionnaires was not overwhelming, although the low kappa values may be explained by the unbalanced marginal totals in all week-by-week tables (16) and the relatively few yes answers after week 10 (17).
Conclusion
Compared with self-administered questionnaires, the interview provided an overall higher response rate and a higher response rate to the specific questions about binge drinking. Furthermore, a higher proportion of women admitted to binge episodes, and the internal consistency was better in the interviews compared with the questionnaires. Self-administered questionnaires are generally easier and cheaper to administer than interviews, and for descriptive purposes the questionnaires may be sufficient to get an overall impression of the distribution of binge drinking. However, if obtaining data in order to study the association between binge episodes during specific weeks and adverse pregnancy outcomes, our results seem to suggest that interviews should be conducted if at all possible, particularly because of high internal consistency.
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ACKNOWLEDGMENTS |
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NOTES |
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REFERENCES |
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