Maternal Recall of Breastfeeding Duration by Elderly Women

Joanne H. E. Promislow1 , Beth C. Gladen2 and Dale P. Sandler1

1 Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC.
2 Biostatistics Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC.

Received for publication May 17, 2004; accepted for publication September 8, 2004.


    ABSTRACT
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Studies of long-term effects of breastfeeding on the health of both infants and mothers often rely on maternal recall of breastfeeding duration after several decades. The authors evaluated this recall by 140 college-educated, US women 69–79 years of age who breastfed a child in 1940–1956 and recorded the duration both prospectively in a diary for the Menstruation and Reproductive History Study and retrospectively in a questionnaire in 1990–1991. Mean prospective breastfeeding duration was 5.6 months (range, 1–12 months). Mean reporting difference, questionnaire minus diary duration, was 0.0 months, with a standard deviation of 2.7 months; women who recorded short durations tended to overreport, while women who noted long durations underreported. The weighted kappa statistic for reporting agreement was 0.55 (95% confidence interval: 0.42, 0.67), with better recall observed for women in the youngest quintile at recall, firstborns, and infants with more siblings. Ever having breastfed was recalled by 94% of women. For categories of 1–3, 4–6, 7–9, and 10–12 months, recalled breastfeeding duration was correctly classified by 54% of women and was classified within ±1 category by 89%. The observed misclassification, if nondifferential with respect to outcome, would appreciably attenuate estimates of dose-response associations between breastfeeding duration and later health.

bias (epidemiology); breast feeding; epidemiologic methods; mental recall; reproductive history; validation studies


Abbreviations: CI, confidence interval.


    INTRODUCTION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The protection that breastfeeding affords against numerous infant illnesses has been well documented (1). Infant nutrition may also have long-term effects. The influence of duration of breastfeeding on adult intelligence (2, 3), obesity (4, 5), serum cholesterol (6, 7), diabetes risk (8), and blood pressure (9, 10) has been the focus of recent studies. Lactation also may influence disease risk for mothers, even decades later. Numerous studies have investigated the influence of duration of lactation on risk of breast (1115) and ovarian (16) cancers and of osteoporosis (1719).

In such studies, breastfeeding history is often assessed by maternal recall, providing the potential for exposure misclassification and biased measures of association. The validity of maternal recall of breastfeeding history has been evaluated in a handful of studies (2028), but most have focused on relatively short-term (≤10 years) recall. The longest known recall period previously evaluated was 20–22 years (20).

The purpose of this study was to assess maternal recall of the duration of a breastfeeding event for elderly US women who breastfed a child and reported the duration both prospectively in a diary and retrospectively in a questionnaire administered 34–50 years later. We evaluated the variation in recall with several maternal and infant characteristics, including maternal age at time of recall, years since event, family size, and infant sex and birth order. In this paper, we discuss the effect of the observed misclassification on measures of association and the implications for interpreting results from studies with long-term retrospective assessment of breastfeeding duration.


    MATERIALS AND METHODS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Participants and protocol
Prospective diary data on breastfeeding duration were obtained from the Menstruation and Reproductive History Study begun in 1934 by Alan Treloar at the University of Minnesota (29). Between 1934 and 1939, 1,807 women younger than age 25 years, primarily White college students, enrolled in this study. Participants prospectively noted menstrual bleeding start and stop dates on the front of annual calendar cards and were asked to record any information concerning events that might influence menstruation, such as lactation, on the back of the cards. Although there were no specific questions about lactation on the calendar card, 173 women prospectively recorded the duration of 310 breastfeeding events. The exclusivity of breastfeeding was not noted.

In 1990, a follow-up study designed to link menstrual characteristics with subsequent health was initiated. The 1,134 women who contributed at least 5 years of menstrual data were eligible for this study. Information necessary for tracing was available for 997, and 943 (94.6 percent) women were successfully located (30). Between 1990 and 1991, a self-administered questionnaire was completed by 716 participants and 158 proxy respondents. For each of their livebirths, participant respondents were asked the following questions pertaining to breastfeeding: "Did you breastfeed?" and "If yes, how many months?" Proxy respondents were not asked for breastfeeding information and consequently were not included in the present analysis.

Of the 716 participants who completed a questionnaire, 407 reported in either the questionnaire or the diary that they breastfed a child, including 147 of the 173 women who prospectively recorded a breastfeeding duration in their diaries. Diary breastfeeding records were matched with questionnaire breastfeeding records by breastfeeding start dates (diary data) and livebirth dates (questionnaire data). Seven women could not be included in the analysis because they did not specify on the questionnaire whether they had breastfed, reported breastfeeding but not the duration, or provided an estimated diary breastfeeding stop date, leaving 140 women for whom 259 matched breastfeeding events occurred between 1940 and 1966. The 259 infants for whom there were prospective records of breastfeeding duration represent just 25 percent of the 1,034 infants reported on the questionnaire to have been breastfed, strongly suggesting that prospective breastfeeding records in the Menstruation and Reproductive History Study are incomplete. Of the women in the final sample, 59 percent kept diary records through menopause.

Statistical analyses
Since both the durations and reporting errors across multiple pregnancies within a woman are likely to be correlated, analyses were restricted to a single breastfeeding event per woman. Analyses were initially performed by using the woman’s first matched breastfeeding event, which took place from 1940 to 1956; all results presented in this paper, unless otherwise noted, derive from these analyses. For comparison, however, the analyses were subsequently repeated by using the women’s last, instead of first, matched breastfeeding event. Of the 140 women in this study, matched diary and questionnaire breastfeeding data for more than one child were available for 72.

Agreement between recalled and prospectively recorded breastfeeding duration was evaluated descriptively with scatter plots and cross-tabulations. Pairwise differences (mean, standard deviation) and the weighted kappa statistic were also computed to evaluate overall agreement and the influence of maternal and infant characteristics. The weighted kappa statistic was calculated by using the Fleiss-Cohen squared error weighting system in which the agreement weight for cell (ij) is given by wij = 1 – ( ij)2/(c – 1)2, with c representing the number of categories. The weighted kappa statistic approximates the intraclass correlation coefficient with this weighting system (31). The values for continuous breastfeeding duration obtained from the diary data were rounded to the nearest month for calculation of the weighted kappa statistic and in all cross-tabulations. Recall of lifetime breastfeeding duration was evaluated in a similar manner for the 45 women who prospectively recorded breastfeeding durations for either each of their livebirths or each of the livebirths that they reported breastfeeding on the questionnaire.

Because the diary data did not differentiate between infants who were not breastfed and infants who were breastfed but for whom that information was not recorded, we could not analyze the specificity with which not breastfeeding is recalled accurately. However, the impact of the observed misclassification error on measures of association between breastfeeding duration and later health was examined by calculating the misclassification-adjusted relative risk estimates for an example dose-response association and reasonable values for both the prevalence of not breastfeeding and the specificity with which not breastfeeding is recalled.


    RESULTS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
There were 226 women who reported a breastfeeding duration on the questionnaire but not in their diaries, despite having been actively keeping prospective records at the time. Compared with these women, the 140 participants in the recall analysis who did prospectively record breastfeeding duration were similar in mean age at follow-up (73.3 years for both groups), had a slightly large mean number of livebirths (3.8 vs. 3.2; p = 0.002), and were more likely to correctly recall the date of their first livebirth (98 percent vs. 88 percent; p = 0.003).

Women for whom there was information in both sources reported breastfeeding durations of 1–12 months in the diary data and 0–12 months on the questionnaire. Eight women, who prospectively recorded breastfeeding durations of 2–8 months, retrospectively reported that they had not breastfed the specified child, giving a sensitivity of 94 percent for recall of having breastfed. Six of these women reported little or no breastfeeding for any of their children on the questionnaire; the other two could possibly have been misreporting which of their children they breastfed. Digit preference at 9 and 12 months was evident in the retrospective data, with women reporting these values 1.8 and 5.0 times as frequently, respectively, in the questionnaire data than in the diary data.

Considerable recall error existed over the range of reported breastfeeding durations (figure 1). The degree of under- and overreporting was very similar overall, with 36 percent and 37 percent of participants doing each, respectively. However, as might be expected, women who prospectively recorded breastfeeding durations of only 1 or 2 months were more likely to recall longer than shorter durations at follow-up. Conversely, women who noted diary durations of ≥9 months were more likely to underreport. Perfect agreement between recorded and recalled months of breastfeeding was obtained for 26 percent of women; 55 percent correctly recalled the duration within 1 month and 71 percent within 2 months.



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FIGURE 1. Plot of breastfeeding duration (months) reported retrospectively on the questionnaire in 1990–1991 versus breastfeeding duration (months) recorded prospectively in the menstrual diary in 1940–1956 by Menstruation and Reproductive History Study participants, United States. The dashed line indicates perfect agreement. Multiple points with identical values were jittered by adding to both coordinates a random number from a normal distribution with a standard deviation of 0.1.

 
In both the diary and the questionnaire data, mean breastfeeding duration was 5.6 months (table 1). The reporting difference, questionnaire minus diary duration, had a mean of 0.0 months (95 percent confidence interval (CI): –0.4, 0.5) and a standard deviation of 2.7 months, indicating substantial misclassification but no overall recall bias. The overall weighted kappa statistic for agreement between diary and questionnaire breastfeeding duration was 0.55 (95 percent CI: 0.42, 0.67). The Pearson correlation coefficient was also 0.55.


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TABLE 1. Agreement between breastfeeding duration reported prospectively in a diary in 1940–1956 by Menstruation and Reproductive History Study participants and retrospectively on a questionnaire in 1990–1991, according to maternal and infant characteristics, United States
 
For the extended recall of 34–50 years, we found no association between time since the lactation event and recall accuracy (table 1). However, recall did appear better for women who were younger at recall, as well as for children from larger families; weighted kappa statistics were 0.33, 0.53, and 0.73 (p = 0.05) for children whose mothers had 1–2, 3–4, and 5–12 livebirths, respectively. The set of first matched breastfeeding events spans a birth order range of 1–7. Recall was better for children born first and, conversely, was worse for children born last.

When the above analyses were repeated by using women’s last matched breastfeeding event instead of their first, similar results were obtained, except that the slightly improved recall seen for female versus male children (table 1) was no longer observed. Overall, recall was slightly less good for the last events, with a weighted kappa statistic of 0.49 (95 percent CI: 0.34, 0.63).

Breastfeeding duration is often categorized. For commonly used categories of 0, 1–3, 4–6, 7–9, and 10–12 months, recalled breastfeeding duration was correctly classified by 54 percent of women and misclassified by one category by 35 percent of them (table 2). Misclassification percentages were higher for women in the shortest (1–3 months) and longest (10–12 months) prospective breastfeeding categories. A common alternative categorization scheme of 0, 1–2, 3–5, 6–8, 9–11, and 12 months was slightly more prone to misclassification, with recalled breastfeeding duration being correctly classified by only 47 percent of women when this scheme was used.


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TABLE 2. Breastfeeding duration reported retrospectively on a questionnaire in 1990–1991 according to breastfeeding duration recorded prospectively in a diary in 1940–1956 by Menstruation and Reproductive History Study participants, United States
 
To illustrate the effect of misclassification on analyses of breastfeeding duration and later health, we calculated the relative risks that would be obtained based on the misclassification observed in table 2 for two breastfeeding prevalence scenarios and two estimates of the specificity with which not breastfeeding is recalled. We assumed that true relative risks were 0.80, 0.60, and 0.40 for breastfeeding durations of ≤3, >3–6, and >6 months versus never breastfed, respectively. For a given breastfeeding duration, misclassification was assumed to be independent of health outcome.

We first used a never-breastfed prevalence of 12 percent. This value was derived by applying the birth-order-specific values for ever breastfeeding rates from the questionnaire data to the birth-order distribution in the first matched event sample. We then repeated the calculations for a much higher never-breastfed prevalence of 50 percent. In both examples, the relative prevalences chosen for the breastfeeding categories of ≤3, >3–6, and >6 months are those observed for the participants included in the recall analyses.

We calculated the estimated relative risks for two values of the specificity with which not breastfeeding is correctly recalled at follow-up, 100 percent and 75 percent. For the latter example, the distribution of recalled breastfeeding durations among women who did not breastfeed was based on values reported in a Brazilian study with recall at a mean child’s age of 47 months (21). The specificity value of 75 percent is likely to be a low estimate, however. Other studies have reported perfect or near perfect recall of not having breastfed (25, 26, 28).

In all four scenarios, the dose-response association was attenuated by the observed misclassification of breastfeeding duration (table 3). For a never-breastfed specificity of 100 percent, the misclassification made the shortest breastfeeding category, ≤3 months, appear more protective than it actually was and the longest breastfeeding category, >6 months, appear less protective than it actually was, thereby weakening evidence for a dose-response association. A true relative risk of 2.0 for breastfeeding ≤3 months versus >6 months was attenuated to a value of 1.4 for both prevalence examples. For a never-breastfed specificity of 75 percent, the misclassification of breastfeeding duration made breastfeeding appear less protective than it actually was across all breastfeeding categories. In all examples, however, the misclassification-adjusted relative risk estimates did remain suggestive of a dose-response association.


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TABLE 3. Effect of misclassification of breastfeeding duration observed among Menstruation and Reproductive History Study participants (United States, 1940–1991) on estimates of relative risk for two breastfeeding prevalence scenarios* and two estimates of the specificity with which not breastfeeding is recalled
 
Evaluation of recall of lifetime breastfeeding duration was possible for 45 women. These women breastfed one to four children (median, two). For this group, mean lifetime breastfeeding duration was 10.4 months in the diary data and 9.9 months in the questionnaire data. The reporting difference mean and standard deviation were –0.5 and 4.7 months, respectively. The weighted kappa statistic for lifetime months of breastfeeding was 0.82 (95 percent CI: 0.72, 0.93). The Pearson correlation coefficient was 0.84. For comparison with the cohort as a whole, the weighted kappa statistic for the first matched breastfeeding event was 0.66 (95 percent CI: 0.50, 0.82) for this more select group.


    DISCUSSION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Because few prospective records exist of breastfeeding history from several decades ago, studies of the long-term health effects of breastfeeding duration on infants and their mothers often rely on retrospective data. Long-term (≥18 years) maternal recall of breastfeeding duration has been used in studies of the association of infant feeding with adult obesity (32), adult vascular function (10), and both child- (33, 34) and adult- (8) onset diabetes. Similarly, studies of lactation and maternal disease, for example, breast cancer (1115), ovarian cancer (16), Hodgkin’s disease (35), and osteoporosis (1719), often rely on maternal recall of the duration of breastfeeding events that ended over 30 years ago. These studies also frequently include women over 70 years of age at the time of recall.

The accuracy of maternal recall of breastfeeding duration after 20–22 years has been investigated in a cohort of Jerusalem residents (20). Other studies have evaluated only relatively short-term (≤10 years) recall (2128), and very little information is available from US women (28). To our knowledge, this study is the first to evaluate maternal recall of breastfeeding duration among elderly US women after more than 30 years.

In this cohort of women who breastfed, we observed appreciable misclassification in breastfeeding duration recalled after 34–50 years. The overall weighted kappa statistic of 0.55 suggests moderate agreement (36) between recalled and prospectively recorded breastfeeding duration. However, for comparison, this value is toward the higher end of the range found for nutrients when comparing food frequency questionnaires with diet records.

Nonetheless, under a number of reasonable scenarios, the observed misclassification would appreciably attenuate a true dose-response association between duration of a breastfeeding event and later health. This attenuation diminishes the ability to detect true weak or moderate dose-response associations and could contribute to some of the inconsistent results reported in the literature. The data on recall accuracy presented here could enable evaluation of the potential effect of measurement error on estimates of the effect of breastfeeding duration, as assessed by maternal recall, on later health of the infant (37, 38).

Previous studies of maternal recall of breastfeeding duration have tended to report better agreement than that observed in this cohort. When their children were 4 years of age, 70 percent of mothers in a Brazilian study correctly recalled breastfeeding duration in the 3-month categories that they had initially reported when their children were 11 months of age (21). In an Australian study, 79 percent of mothers correctly recalled duration of breastfeeding within 1 month at a mean child age of 3 years (25). Other studies have reported correlation coefficients of 0.94 and 0.86 for the association between prospectively recorded breastfeeding duration and that recalled by mothers after 8 and 20 years, respectively (20, 22). Median breastfeeding duration was shorter in each of these previous studies than in the current study, and some of the previous studies included a small proportion of women (≤10 percent) who did not breastfeed, which could have affected the measures of agreement and association. However, the substantially longer recall period and older age at time of recall seem probable reasons for the reduced agreement observed in this study.

Huttly et al. (21) reported that maternal recall of breastfeeding duration was less accurate after 3 years than after 1 year. In contrast, recall accuracy did not differ over recall periods of 34–50 years in this study, suggesting an earlier plateau in the decline in recall accuracy. However, even over the limited age range of 69–79 years, there was some evidence to suggest that younger women had better recall, consistent with the increasing prevalence of memory problems with age.

To our knowledge, the influence of family size on recall of breastfeeding duration has not been reported previously; however, recall of birth weight has been found to decrease among mothers with five or more children (39). Surprisingly, in this study, agreement was found to improve with increasing family size. This effect could derive from enhanced recall by mothers who maintained similar breastfeeding patterns for multiple children. Prospectively recorded breastfeeding durations for first and second births were positively correlated (Pearson correlation coefficient = 0.52).

In the Brazilian study, better educated women were more likely to recall a longer breastfeeding duration than originally reported (21). In the present study of predominantly college-educated women, no overall bias toward over- or underreporting breastfeeding duration was observed either for the cohort as a whole or for any specific maternal or infant characteristic. Maternal recall of child-rearing practices has been reported to err in the direction of experts’ recommendations (28). While the American Academy of Pediatrics now recommends breastfeeding for ≥12 months (1), expert support for extended breastfeeding was less pronounced both when participants breastfed and at follow-up (40). The tendency for participants who breastfed for 9–12 months to underreport at follow-up may instead reflect societal norms at the time and the perceived social stigma associated with extended breastfeeding (41).

For studies evaluating the effect of lactation on later maternal health, recall of lifetime lactation may be most relevant. The higher kappa value found for recall of lifetime lactation probably reflects improved recall correlation due to both the greater variation between women in lifetime lactation and the increased selectivity of the subset of women for whom this analysis could be performed.

This study has some limitations. Recall of neither not breastfeeding nor exclusive breastfeeding could be evaluated. Additionally, study participants prospectively noted breastfeeding duration without being specifically prompted and might therefore reflect a selective subset of the follow-up cohort. Indeed, compared with women who reported breastfeeding retrospectively but not prospectively, women who did keep prospective breastfeeding records had significantly better recall of the date of their first livebirth, suggesting that the recall observed in this study might be better than average.

The absence of specific breastfeeding questions in the menstrual diaries also raises the possibility that some women may no longer have noted continued lactation once menses resumed. A prospective breastfeeding stop date within 1 month after the date menses resumed was recorded for only 27 of the 82 women with a breastfeeding stop date on (three women) or after the date menses resumed, however. This possible limitation also runs counter to the observation that women who noted longer prospectively recorded breastfeeding durations tended to underreport at follow-up. Study participants were also predominantly college-educated Whites from Minnesota who had demonstrated motivation for record keeping and who breastfed the children included in the analysis between 1940 and 1956, further limiting the generalizability of these results to other populations.

The appreciable misclassification observed in this cohort of older US women suggests that if misclassification is independent of disease status for a given breastfeeding duration, observed dose-response associations between breastfeeding duration and later health are likely to underestimate the true associations and that weak or moderate associations may be difficult to detect. Recall patterns in this cohort also suggest that after several decades, time since event may be a less important predictor of accuracy than age at recall. The better recall of breastfeeding duration observed for firstborns and children from larger families is intriguing and merits further investigation.


    ACKNOWLEDGMENTS
 
The authors are grateful to the late Dr. Alan Treloar, who conceived of and developed the Menstruation and Reproductive History Study, and to Dr. Ann Voda, former Director of the Tremin Trust Research Study, for her permission to contact women from the study. The authors also thank Drs. Ken Smith, Jan Root, and Elizabeth Whelan for their work in assembling and tracing the cohort and Drs. Donna Baird and Walter Rogan for their comments on the manuscript.


    NOTES
 
Correspondence to Dr. Joanne Promislow, National Institute of Environmental Health Sciences, P.O. Box 12233, MD A3-05, Research Triangle Park, NC 27709 (e-mail: promisl1{at}niehs.nih.gov). Back


    REFERENCES
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Breastfeeding and the use of human milk. American Academy of Pediatrics. Work Group on Breastfeeding. Pediatrics 1997;100:1035–9.[Abstract/Free Full Text]
  2. Gale CR, Martyn CN. Breastfeeding, dummy use, and adult intelligence. Lancet 1996;347:1072–5.[ISI][Medline]
  3. Mortensen EL, Michaelsen KF, Sanders SA, et al. The association between duration of breastfeeding and adult intelligence. JAMA 2002;287:2365–71.[Abstract/Free Full Text]
  4. Parsons TJ, Power C, Manor O. Infant feeding and obesity through the lifecourse. Arch Dis Child 2003;88:793–4.[Abstract/Free Full Text]
  5. Victora CG, Barros F, Lima RC, et al. Anthropometry and body composition of 18 year old men according to duration of breast feeding: birth cohort study from Brazil. BMJ 2003;327:901.[Abstract/Free Full Text]
  6. Marmot MG, Page CM, Atkins E, et al. Effect of breast-feeding on plasma cholesterol and weight in young adults. J Epidemiol Community Health 1980;34:164–7.[Abstract]
  7. Fall C. Nutrition in early life and later outcome. Eur J Clin Nutr 1992;46(suppl 4):S57–63.[Medline]
  8. Pettitt DJ, Forman MR, Hanson RL, et al. Breastfeeding and incidence of non-insulin-dependent diabetes mellitus in Pima Indians. Lancet 1997;350:166–8.[CrossRef][ISI][Medline]
  9. Owen CG, Whincup PH, Gilg JA, et al. Effect of breast feeding in infancy on blood pressure in later life: systematic review and meta-analysis. BMJ 2003;327:1189–95.[Abstract/Free Full Text]
  10. Leeson CPM, Kattenhorn M, Deanfield JE, et al. Duration of breast feeding and arterial distensibility in early adult life: population based study. BMJ 2001;322:643–7.[Abstract/Free Full Text]
  11. London SJ, Colditz GA, Stampfer MJ, et al. Lactation and risk of breast cancer in a cohort of US women. Am J Epidemiol 1990;132:17–26.[Abstract]
  12. Newcomb PA, Storer BE, Longnecker MP, et al. Lactation and a reduced risk of premenopausal breast cancer. N Engl J Med 1994;330:81–7.[Abstract/Free Full Text]
  13. Michels KB, Willett WC, Rosner BA, et al. Prospective assessment of breastfeeding and breast cancer incidence among 89,887 women. Lancet 1996;347:431–6.[CrossRef][ISI][Medline]
  14. Newcomb PA, Egan KM, Titus-Ernstoff L, et al. Lactation in relation to postmenopausal breast cancer. Am J Epidemiol 1999;150:174–82.[Abstract]
  15. Freudenheim JL, Marshall JR, Vena JE, et al. Lactation history and breast cancer risk. Am J Epidemiol 1997;146:932–8.[Abstract]
  16. Tung KH, Goodman MT, Wu AH, et al. Reproductive factors and epithelial ovarian cancer risk by histologic type: a multiethnic case-control study. Am J Epidemiol 2003;158:629–38.[Abstract/Free Full Text]
  17. Gur A, Cevik R, Nas K, et al. The influence of duration of breastfeeding on bone mass in postmenopausal women of different age groups. Int J Clin Pract 2003;57:82–6.[ISI][Medline]
  18. Kojima N, Douchi T, Kosha S, et al. Cross-sectional study of the effects of parturition and lactation on bone mineral density later in life. Maturitas 2002;41:203–9.[CrossRef][ISI][Medline]
  19. Huo DZ, Lauderdale DS, Li LM. Influence of reproductive factors on hip fracture risk in Chinese women. Osteoporos Int 2003;14:694–700.[CrossRef][ISI][Medline]
  20. Kark JD, Troya G, Friedlander Y, et al. Validity of maternal reporting of breast feeding history and the association with blood lipids in 17 year olds in Jerusalem. J Epidemiol Community Health 1984;38:218–25.[Abstract]
  21. Huttly SRA, Barros FC, Victora CG, et al. Do mothers overestimate breast feeding duration? An example of recall bias from a study in southern Brazil. Am J Epidemiol 1990;132:572–5.[Abstract]
  22. Vobecky JS, Vobecky J, Froda S. The reliability of the maternal memory in a retrospective assessment of nutritional status. J Clin Epidemiol 1988;41:261–5.[ISI][Medline]
  23. Launer LJ, Forman MR, Hundt GL, et al. Maternal recall of infant feeding events is accurate. J Epidemiol Community Health 1992;46:203–6.[Abstract]
  24. Bland RM, Rollins NC, Solarsh G, et al. Maternal recall of exclusive breast feeding duration. Arch Dis Child 2003;88:778–83.[Abstract/Free Full Text]
  25. Eaton-Evans J, Dugdale AE. Recall by mothers of the birth weights and feeding of their children. Hum Nutr Appl Nutr 1986;40:171–5.[Medline]
  26. Goddard KE, Broder G, Wenar C. Reliability of pediatric histories. A preliminary study. Pediatrics 1961;28:1011–18.[Abstract]
  27. Haggard EA, Brekstad A, Skard AG. On the reliability of the anamnestic interview. J Abnorm Soc Psychol 1960;61:311–18.[ISI][Medline]
  28. Robbins LC. The accuracy of parental recall of aspects of child development and of child rearing practices. J Abnorm Soc Psychol 1963;66:261–70.[Medline]
  29. Treloar AE, Boynton RE, Behn BG, et al. Variation of the human menstrual cycle through reproductive life. Int J Fertil 1967;12(1 pt 2):77–126.
  30. Root J, Smith KR, Whelan EA, et al. Tracing women over half a century. Res Aging 1994;16:375–88.[ISI]
  31. Fleiss JL, Cohen J. The equivalence of weighted kappa and the intraclass correlation coefficient as measures of reliability. Educ Psychol Meas 1973;33:613–19.[ISI]
  32. Kramer MS. Do breast-feeding and delayed introduction of solid foods protect against subsequent obesity? J Pediatr 1981;98:883–7.[ISI][Medline]
  33. Kostraba JN, Dorman JS, LaPorte RE, et al. Early infant diet and risk of IDDM in blacks and whites. A matched case-control study. Diabetes Care 1992;15:626–31.[Abstract]
  34. Mayer EJ, Hamman RF, Gay EC, et al. Reduced risk of IDDM among breast-fed children. The Colorado IDDM Registry. Diabetes 1988;37:1625–32.[Abstract]
  35. Glaser SL, Clarke CA, Nugent RA, et al. Reproductive factors in Hodgkin’s disease in women. Am J Epidemiol 2003;158:553–63.[Abstract/Free Full Text]
  36. Altman DG. Practical statistics for medical research. London, United Kingdom: Chapman and Hall, 1991:404–9.
  37. Rosner B, Willett WC, Spiegelman D. Correction of logistic regression relative risk estimates and confidence intervals for systematic within-person measurement error. Stat Med 1989;8:1051–69; discussion 1071–3.
  38. Spiegelman D, McDermott A, Rosner B. Regression calibration method for correcting measurement-error bias in nutritional epidemiology. Am J Clin Nutr 1997;65:1179S–1186S.[Abstract]
  39. Burns TL, Moll PP, Rost CA, et al. Mothers remember birthweights of adolescent children: The Muscatine Ponderosity Family Study. Int J Epidemiol 1987;16:550–5.[Abstract]
  40. Spock B. Baby and child care. New York, NY: Pocket Books, 1957.
  41. Reamer SB, Sugarman M. Breastfeeding beyond six months: mothers’ perceptions of the positive and negative consequences. J Trop Pediatr 1987;33:93–7.[ISI][Medline]




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