1 Department of Family Medicine and Community Health, School of Medicine, Tufts University, Boston MA.
2 Epidemiology Program, Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, MA.
3 Calcium and Metabolic Bone Laboratory, Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, MA.
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ABSTRACT |
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anthropometry;; body image;; body mass index;; menarche;; menstruation;; recall;; somatotypes
Abbreviations: BMI, body mass index;; NGS, Newton Girls Study.
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INTRODUCTION |
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Menarcheal characteristics of interest in women's health include age at menarche, age at cycle regularity, and menarcheal weight status. Early age at menarche is an established risk factor in the development of breast cancer (14
) and has also been associated with uterine leiomyomata (5
) and endometrial cancer (6
).
The number of ovulatory cycles before the first pregnancy has been linked to breast cancer risk (7, 8
) and may explain why early menarche increases this risk. Other menstrual characteristics, such as cycle regularity, appear to be related to the number of ovulatory cycles and, thus, may also represent potential breast cancer risk factors. Extremes of cycle length increase the risk of ovulatory infertility (3
). A major source of cycle length variation occurs during the first 2 years after menarche (9
13
). Furthermore, girls who establish regular cycles early are more likely to be ovulating than girls who remain irregular.
Physical characteristics, such as weight and height in childhood and adolescence, can also have an impact on adult health. Earlier age at which maximum height is achieved (14, 15
) and peak height growth velocity (16
) may increase breast cancer risk. Protective effects of elevated preadolescent and adolescent weight status have been reported for breast cancer occurrence (16
18
) and for increased adult bone mineral density (19
). Obesity present during puberty may be an independent risk factor for other reproductive problems, such as polycystic ovary syndrome and infertility (20
). In addition, obesity present in childhood and adolescence represents a major pathway to other adverse health consequences, such as coronary heart disease, type 2 diabetes, and hypertension because of the likelihood that early obesity will persist (21
, 22
).
Some of the inconsistencies observed in the relation between early menstrual characteristics and long-term consequences may stem from reliance on remote recall. Early menstrual regularity and short or long menstrual cycle length have been associated with breast cancer in some (2326
), but not all (1
, 27
), studies. Garland et al. (3
) suggest that the inconsistent results from case-control studies of the interval between menarche and the establishment of regular cycles in relation to breast cancer may be due to difficulty in recall. Such misclassification would bias effect estimates toward the null. So-called "validation" studies of recall have been undertaken with differing intervals between menarche and recall and with various measures of error (28
32
). Much of this research has been done using historical cohorts. Less is known about the validity of other menstrual characteristics, such as cycle length and age at regularity.
The original materials of the Newton Girls Study (NGS) provided the rare opportunity to assess the validity of long-term recall of early menstrual characteristics among a cohort of women nearing menopause. Menstrual cycle data are inherently complex and present the researcher with substantial challenges. To assess the precision and accuracy with which middle-aged women recall their menarcheal age, cycle length, and body size at menarche, we developed and applied a set of analytical approaches.
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MATERIALS AND METHODS |
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Adult data
In 1998, up to 33 years after the original NGS, recontact with the original study subjects was undertaken to collect recalled information on early menstrual characteristics. Efforts to locate NGS participants included the use of the Massachusetts Department of Public Health Vital Statistics Office, alumni books for the Newton high schools, voting books from Newton City Hall, Internet address locators, and credit bureau searches. Because this cohort is composed entirely of women, identifying married names was essential to location efforts. An initial contact letter and response card were sent through the mail to the subject or, if no address for the subject was available, to one of her parents or siblings. Up to three repeat mailings were sent to confirmed addresses. For assurance that the subject was unaware of the hypothesis under study, the letter described the study as an investigation of the relation between early growth and later women's health outcomes. Once the subject returned a postcard agreeing to participate, she was sent a health questionnaire to be completed and returned. The protocol was approved by the Tufts-New England Medical Center Human Investigation Review Committee.
Of the original 793 participants, 1 percent (n = 9) were deceased at the time of follow-up or were unable to respond due to poor health. Of the remaining 784 women, 57 percent (n = 448) completed the mailed questionnaire, 6 percent (n = 44) declined participation, and the remaining women could not be located (n = 50) or did not respond to repeated mailings to a verified address (n = 242). The follow-up questionnaire asked women to recall their age at menarche, the age at which their periods became regular, and their body size at menarche by using figure drawings. In addition, the questionnaire asked for recall of usual cycle length during the first 2 years of menstruation. The information provided by these 448 respondents constitutes what we refer to as "recalled" measurements obtained from the follow-up questionnaire.
Variables
A set of variables was developed to allow for the comparison of original and recalled measurements. Original age at menarche was extracted from the original records. Original body mass index (BMI) percentile at menarche was calculated from height and weight reported at menarche in reference to the First National Health and Nutrition Examination Survey (36). Original measures of cycle length were extracted from the original data for subjects with adequate data during the first 2 years. Age at regularity was determined from the original data by applying the definition used by the World Health Organization Task Force on Adolescent Reproductive Health (11
). A girl was considered to have reached regularity when the lengths of three consecutive cycles were within a range (maximum minimum) of 10 days and all three cycles were between 20 and 40 days. The girl's age at the period marking the first of these three consecutive periods was taken as the age at regularity.
Women were asked to recall their age at menarche and at regularity in years and months. They were also asked to report whether or not their periods ever became regular (at any point in their lives) and, if they became regular, the age at which regularity was reached. Because most women participated in the original study only for a maximum of 2024 menstrual cycles (approximately 2 years), age at regularity could be assessed only for those women who reached regularity during the first 2024 cycles postmenarche. In addition, women were asked to recall usual cycle length and regularity during the first 2 years of menstruation. Women were also asked to recall their body size at ages 10, 12, 14, 16, and 18 years by using figure drawings ranked from one to nine (37). The drawing corresponding to the age that was closest to the originally reported age at menarche was taken to reflect the subject's recalled body size at menarche.
The original and recalled variables described above were used to assess the accuracy and precision with which women recall their early menstrual characteristics. Recalled age at menarche was subtracted from original age at menarche to compute error in recall of menarcheal age. Similarly, recalled average cycle length was subtracted from original mean, median, or modal cycle length to compute error in recall of cycle length. A BMI percentile was established for each drawing based on expert opinion (38). The percentiles used were developed based on the First National Health and Nutrition Examination Survey, conducted from 1971 to 1973 (39
). The subjects in the study were born in 19551957 and, thus, would have been early adolescents at the time of the Survey.
To assess the error in recall of body size at menarche, we compared these BMI percentiles associated with the drawing selected based on recall to the subject's BMI percentile calculated from original height and weight recorded at menarche.
Analysis
Data were analyzed using SPSS 9.0 (SPSS, Inc., Chicago, Illinois) and S-Plus (Insightful, Seattle, Washington). Statistical significance was set at p < 0.05, and two-sided tests were conducted throughout. Student's t tests were used to compare menstrual characteristics between respondents and nonrespondents.
The analytical techniques selected reflect the nature of the data and our particular goals: to evaluate the potential for random misclassification (lack of precision) and bias (lack of accuracy). Pearson and Spearman correlation coefficients were used to examine the association (likelihood of misclassification) between recalled and original menarcheal age and body size at menarche. We also examined the conditional distribution of original BMI percentile for a given recalled body size by using box plots. Linear regression modeling was used to assess the impact of current BMI and early menstrual characteristics on recall of age and body size at menarche.
The potential for bias was explored by examining the disparity between original and recalled measurements. To assess the difference between original and recalled measures (error), we conducted paired t tests for continuous variables (menarcheal age and age at regularity). To explore how recall error varied across the range of original values, we examined the relation between error in recall of menarcheal age, BMI percentile at menarche, and age at regularity. For each of the measures, we also calculated an absolute error (|recalled original|), which reflects its magnitude of disparity and related it to the original value of the measurement. To examine the shape of these relations for error and for absolute error, we used a generalized additive model (40) with a Loess smoother as an additive contributor. We plotted the predicted error (or absolute error) and its 95 percent confidence interval against the original BMI measurement. For assessment of the measure of central tendency most accurately related to recalled cycle length, error in recall of cycle length (recalled original) was compared with the original mean, median, and modal cycle length.
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RESULTS |
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On average, women recalled their menarche as being 0.08 years earlier than their original menarche (95 percent CI: 0.18, 0.01). However, the mean absolute error in recall (|recalled original|) was 0.62 years on average and varied considerably and nonlinearly across menarcheal ages (figure 1). The smoothed curve for the absolute error and its 95 percent confidence interval (obtained from a generalized additive model) ranged from about 0.4 to 0.8 years and increased sharply after the average age at menarche (about 12.9 years). The error continues to exceed the average of 0.62 years until about age 16 years.
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Recall of body size at menarche
Figure 2 presents a plot of recalled body size and the corresponding distribution of measured BMI percentile at menarche. Although the possible body sizes ranged from one to nine, no women recalled a body size of greater than seven. More than half of the women who recalled their body size as three were above the 50th percentile BMI, and more than three quarters of those who recalled their body size as four were above the 50th percentile. Variability in BMI percentile at menarche decreased markedly across increasing recalled body sizes. Overall, BMI percentile at menarche was well correlated with recalled body size at menarche (Spearman's r = 0.61; p < 0.001).
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Recall of early cycle length during the first 2 years
Almost all subjects (91 percent) became regular during the first 2 years after menarche. The error in recall of early cycle length was examined for the three basic measures of central tendency: the mean, median, and mode of original cycle lengths over the first 2 years of menstruation. The recall error for each is presented stratified by original and recalled regularity, yielding four estimates (table 4). The three central tendency measures gave very different estimates of recall error. The recall of regularity does not correspond well with the mean or median cycle lengths during the first 2 years as calculated from the original measurements, with recall errors of 9.27 days (mean) and 3.67 days (median) for subjects who recalled being regular. In contrast, for subjects who recalled that their periods were regular during the first 2 years, the recall of cycle length is accurately recalled, with an average error of 0.24 days, when compared with the original modal cycle length.
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DISCUSSION |
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Our findings with regard to the accuracy of recall of menstrual characteristics confirm and extend the findings reported in other studies (2832
, 41
, 42
42). Previous studies of the recall of age at menarche report correlation coefficients of 0.600.81 (28
31
, 41
), a surprisingly narrow range given that the studies reflect recall intervals of 139 years. In those studies for which a mean recall error is reported, mean errors were lower than 0.5 years (28
,
32
, 42
), and these small differences were often not different statistically. In our study, we found that recall of age at menarche was generally quite good, both in precision (r = 0.79) and accuracy (mean error (recalled original) 5 0.08 years). The average absolute error better describes the degree to which individual measures deviate from the true measure and will often be more informative than the correlation or mean difference between the recalled and original measures. Further, our study evaluated this error across menarcheal ages and found it to be nonlinear: Absolute error was smallest for menarche that occurred earlier than the mean for the cohort (12.9 years). Error also appeared to decline for older ages at menarche (>16 years), but the sparseness of data at the older ages makes it difficult to draw any conclusion for this group. Given that early menarche is often of interest as a risk factor in studies of cancers of reproductive organs, our data suggest that recalled measures of age at menarche should be quite valid.
Consistent with expectations, research on memory formation indicates that recall ability is directly related to the salience of the event for the respondent (43) and that important personal experiences can produce clear memories of a person's circumstances at the time of the event, so called "flashbulb memories" (44
). Our finding that early menarche was well recalled is in keeping with the idea that events that disrupt personal plans aid memory formation. College women who recalled that they were less knowledgeable about menstruation provided more information about the first episode, presumably because the event was somewhat traumatic (45
).
Recall of body size around the time of menarche is particularly challenging since height and weight are changing during childhood because of growth; subjects are unlikely to recall their height and weight at a given age. Many epidemiologic studies substitute a weight recalled at age 18 or 20 years to reflect adolescent weight status (46, 47
). However, if weight status around puberty is the exposure of interest, this compromise may obscure the true relations.
Casey et al. (28) assessed the precision and accuracy of long-term recall of body fatness "relative to peers" during early adolescence for females and found moderately strong correlations (r = 0.79) and that the percentage of correct classifications for males and females together (approximately 60 percent) did not vary by maturational timing. Both men and women tended to underestimate their relative fatness during early adolescence. The precision of recalled body size in our study was also fairly good, with a correlation of 0.61. The figure drawings we used in our study are currently used to assess past body size in several large, ongoing prospective studies, including the Nurses' Health Study (48
), the Health Professionals Follow-Up Study (49
), and the Harvard Alumni Studies (R. S. Paffenbarger, Jr., Harvard School of Public Health, personal communication, 2000). Our previous examination (50
) of the validity of these drawings to reflect adolescent BMI recalled after many years yielded similar results, with correlations of 0.65 (at age 10 years) and 0.75 (at age 15 years). Although coefficients of 0.600.75 are generally considered to indicate that two measures are well correlated (51
), in the recall context, the strength of this relation can be easily misinterpreted. If our interest is to assess the quality of recall across the entire range of values, the regression approach is preferable.
Our available data did not allow us to directly assess bias in recall of body size, but use of expert opinion permits us to explore the nature of recall error. We observed systematic bias: For all but the thinnest girls, subjects underestimated their body size, and the magnitude of the error increased with increasing original BMI percentile.
The literature on the recall of other menstrual characteristics is quite sparse, probably due to the paucity of data sets with the appropriate early measurements. In a sample of 160 subjects in three adult age groupings selected from the Menstrual and Reproductive History Study cohort, several menstrual characteristics, including age at menarche, menstrual cycle length, and cycle variability, recalled during a face-to-face interview were compared with historically recorded data. Cycle length and variability were poorly recalled, with percentage agreements of less than 60 percent for both measures at all ages (32). It is difficult to compare these findings with the current ones because the measure of cycle variability was not comparable with the World Health Organization definition of regularity we used. Furthermore, because the Menstrual and Reproductive History enrolled women during their college years, their earliest recorded periods are for cycles before age 20 years, not for the first 2 years of menstruation, which are generally more variable.
Our evaluation of the concordance of recalled cycle length to original mean, median, and modal cycle lengths suggests that when asked to recall "average cycle length," women report the mode. We conclude that researchers who wish to obtain a measure of cycle length would do well to ask a pair of questions, in which past cycle length is asked only for women who recall that they were regular. The information supplied in this context is apt to reflect the modal cycle length.
This study has a number of noteworthy limitations. First, participation in the original study may have influenced recall. In the original study, all questionnaires and communications were addressed to the mothers to ensure a more reliable and systematic return of the questionnaires and to reduce misreporting due to a girl's desire to be like her classmates. However, later in the study, the girls themselves often provided the information. If participation enhanced recall, one would expect that our findings represent the best-case scenario for remotely recalled measures of early menstrual characteristics. We did exclude data for one study subject who provided us with a lifetime log of every menstrual period she had experienced since menarche. Unfortunately, we did not have data on comorbidity during menarche, which could have influenced the timing of onset or patterns. In addition, the subjects in this study were White, well-educated women, so our findings may not be directly generalizable to women of other races or with lower educational attainment. However, we believe that this inquiry has particular relevance to women's health issues because it is this age group of women who are entering a life stage of increased risks for breast cancer, osteoporosis, and cardiovascular diseases. Furthermore, our study population was predominantly Jewish (based on maiden surname) and professional, both of which are characteristics associated with higher breast cancer risk (52).
In conclusion, epidemiologists interested in menstrual data as exposure measures will probably continue to rely on retrospectively collected data, given the expense and subject burden associated with gathering such data prospectively. Our experience with this rich data set suggests that long-term recall of age and relative weight status at menarche are quite valid as exposure measures. We believe that information on cycle length can be validly obtained only for women who report that they are regular. Our analyses sought to emphasize the importance of assessing both misclassification and bias and their independent contributions to validity.
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ACKNOWLEDGMENTS |
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NOTES |
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REFERENCES |
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