Reviewer ’s report  
 
Title: THE REPRODUCIBILITY OF SELF -REPORTED AGE AT MENARCHE. THE  
TROMSØ STUDY  
 
Version: 0 Date: 17 Apr 2017  
 
Reviewer: Brian Whitcomb  
 
Reviewer's report:  
 
Summary: As described by the authors, self -report of age at menarche is commonly used in large 
epidemiologic research studies. The authors describe that prior literature evaluating self -report of 
age at menarche show high to moderate validity and that studies of reliability are limited by low 
numbers of particip ants, short time of recall, and limits in the ages of included participants. In 
the current manuscript, the authors utilize data on self -reported age at menarche from 6,731 
women from the Tromso study at two time points approximately 7 years apart (1986 -7 and 1994 -
5). Participants ranged in age from 25 to 73 in 1994. The mean self -reported age at menarche at 
both time points was 13.2 and the mean age of participants was 45.3 years of age; accordingly, 
initial self -reported age at menarche by participants te nded to have occurred more than 30 years 
after menarche itself. The authors use Pearson correlation coefficients to show linear correlation 
of self -reported age at menarche at the two time points seven years apart overall and stratified by 
age group, and B land-Altman plots to illustrate differences in self -report. Analyses yielded a 
correlation coefficient estimate of 0.84 overall; in stratum specific estimates, correlation 
coefficients were 0.81 in the youngest age group (25 -34 years of age) and highest in  the oldest 
age group of women 65 -74 years of age (r=0.91).  
 
 
Comments: The paper is well written and the analysis and results are clearly described. Based on 
these data, which comprise repeated measures of self -reported age at menarche collected at a 
fixed interval, the authors effectively describe measures of agreement as a reflection of reliability 
overall and within strata of age.  
 
 
Prior reliability studies that evaluated the consistency of recalled age at menarche at multiple 
time points have been mor e or less in agreement that self -report has moderate to high 
reproducibility, as the authors note. Validity has been considered by prior research as well, 
however. As cited by the authors, Must et al. (2002) observed age at menarche reported at 
menarche to  have high correlation (r=0.79) with recalled self -report up to 33 years later among 
448 participants in the Newton Girls Study. In an even larger study sample, Cooper et al. (2006) 
observed a slightly lower correlation (r=0.61) of age -at-menarche reported  in adolescence with 
self-report at 48 years of age among 1050 women from the Medical Research Council National 
Survey of Health and Development. Given results of prior research regarding validity of age at 
menarche self -reported in midlife, and those of s tudies regarding consistency of repeated self -
reports, the results of this study do not seem surprising. The current manuscript builds on prior 
studies though use of a dataset with substantially greater sample size than most previous reports, 
and that incl udes women with a wide age range so that 7 year reliability was able to be compared 
by age group. The observation that older women had a higher inter -report agreement is 
potentially overstated, being based on only 65 women, but is not inconsistent with the  generally 
high correlations observed for the study sample as a whole. Although the data do not include 
age-at-menarche reported at time of menarche to use to evaluate validity of self -report by women 
across a range of ages, the observation of similar corr elations across the wide age range of 
participants may be useful information to investigators who utilize self -reported age at menarche 
to help provide context to results. Still, given prior studies, including those of validity with very 
long periods betwe en reports and those of reliability, it is important for the authors to be clear 
about what their work contributes.  
 
 
 
Specific comments:  
 
Line 37: language - 'not attenuated by the age of the women'. Do the authors mean that the 
correlation of report at th e two time points was not attenuated in analyses that addressed age?  
 
 
Line 40: The conclusion seems a little terse. Perhaps expand upon this somewhat?  
 
 
Line 50: grammar - "…a significant event, which have…"  
 
 
Line 52: grammar - "…a trend toward a lower mea n age at menarche have…"  
 
 
Line 60: grammar - "…life, the information about…". Delete "the"  
 
 
Line 69: The authors cite [6 -8] regarding validity. First, including these and the more recent 
Cooper et al. 2006, can the authors provide more specific information  regarding measures of 
validity and the sample sizes for these studies? Second, given what has been suggested regarding 
validity, can the authors provide comment on the utility of assessment of reproducibility of a 
variable such as age -at-menarche, which i s does not have any temporal instabililty? Why is 
"there is a need for larger studies that both provide the opportunity for assessing the 
reproducibility of women with different age and with a relatively long period between the data 
collections" (line 81)?   
 
 
Line 73: grammar: "…with one -year interval." Should be 'intervals'  
 
 
Line 76: the authors note short time between recalls here as a limitation. Can the authors provide 
more detail on the time between recall assessed previously?  
Line 98: "…how old they were in years…" Is it correct that AAM was recalled as an integer 
only, and not fractions? How does this compare with how age -at-menarche is collected in other 
studies of self -report? Assuming this is the case, the authors might con sider as an additional 
figure showing self -report at Tromso 3 cross -tabulated by that at Tromso 4. Because of the 
nature of the data (integers collected at only 2 time points) there is a great deal of overlap in the 
points on the plot and the relative weig ht of the points is hard to resolve. A cross -tabulation 
would allow readers to more clearly see the actual data, concordance, and magnitudes of 
discordance. This might nicely complement the age -stratified summary results shown in the 
table.  
 
 
Line 178: The authors note the presence of only 5 outliers with a 6 -year difference between 
reports. Though a 6 year disagreement is intriguing, the infrequent occurrence of this makes it of 
little note. On the other hand, smaller amounts of disagreement are of greater note, perhaps. 
Again, the plot does not reflect the frequency of these disagreements very well. Given that AAM 
was collected as an integer, the difference between women's self -reports at the two time points 
had to be an integer, as well, as is clearly show n by the banding in the Bland -Altman plot. Given 
the data, beyond the limits of agreement, it might be of interest to know proportions with 
disagreement greater than 1 year (as shown in the table), 2 years, etc.  
 
 
Line 184: The statement "this correlation s trengthened with increasing age" is based on a point 
estimate from a very small group of women, and seems overstated. Moreover, there does not 
seem to be a clear explanation why women in the oldest age group would be the most accurate in 
their recall and, if not, what higher reproducibility for repeated recalls would imply.  
 
 
Line 216: Can the data be used to provide comment on the tendency of women whose two 
reports do not concur to be adjusted toward what might be perceived as "normal"? It appears that 
roughly 40% of women were not perfectly concordant in their reports, but it is hard to tell from 
the table the relative frequencies of women's second report to be closer or further from 13 years 
of age.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Are the methods appropriate and well described?  
If not, please specify what is required in your comments to the authors.  
 
Yes 
 
Does the work include the necessary controls?  
If not, please specify which controls are required in your comments to the authors.  
 
Yes 
 
Are the conclusions drawn adequately supported by the data shown?  
If not, please explain in your comments to the authors.  
 
Yes 
 
Are you able to assess any statistics in the manuscript o r would you recommend an  
additional statistical review?  
If an additional statistical review is recommended, please specify what aspects require further  
assessment in your comments to the editors.  
 
I am able to assess the statistics  
 
Quality of written Englis h 
Please indicate the quality of language in the manuscript:  
 
Needs some language corrections before being pu blished  
 
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