Reviewer ’s report  
 
Title: THE REPRODUCIBILITY OF SELF -REPORTED AGE AT MENARCHE. THE  
TROMSØ STUDY  
 
Version: 0 Date: 05 Dec 2016  
 
Reviewer: Aw Froehle  
 
Reviewer's report:  
 
I think this is an interesting and well -conducted study on an excellent dataset, and overall I 
would recommend publication. I do have some minor suggestions, as well as recommending 
substantial revision of the statistic al methods used. I will present my minor concerns first, and 
then outline what I would recommend statistically.  
 
 
1. The paper is well -written overall, but there are consistent verb conjugation errors that 
should be corrected prior to publication.  
 
 
 
2. Metho ds: did any subjects have any access to their first responses in the period between 
questionnaires, for example in the form of copies of their data that they may have been 
given? This could certainly have influenced their second responses if they "studied"  prior 
to the Tromso4 visit, so if they had no such access, it is important to report that.  
 
 
 
3. Discussion, page 9 line 211. There is no basis for the claim that these data are accurate, 
since there is no independent verification/observation of age at mena rche outside of the 
self-report, which is somewhat error -prone (the reporting of age as an integer in and of 
itself introduces up to 364 days of error if menarche is considered to be the first episode 
of menstrual bleeding, since that occurs on a single da y). While you have demonstrated a 
high degree of reproducibility, the original answer could very well be inaccurate even if 
reproducibly stated as the same inaccurate age at both questionnaire time points. I would 
remove the word "accurate" from that sente nce. 
 
 
 
4. Statistical analysis: First, I think the use and interpretation of the Bland Altman plot is 
largely sound, but I do think that more attention needs to be paid to the fairly wide limits 
of agreement. The 95% range covers 3 years, which is, dependin g on who you ask, up to 
~60% of the range of "normal" age at menarche. For any study examining variation in 
some other variable as a function of recalled age at menarche, that level of error could be 
important. Although the mean difference in reported ages  is small, the variability around 
that mean seems fairly high, so I would include further discussion of what that could 
mean for studies using recalled age at menarche as a covariate or factor in an analysis.  
 
 
The more important statistical issue I have is  with the use of Pearson correlation and the informal 
manner in which age at report (age at Tromso4) was analyzed. These are repeated measures, 
meaning that there is correlation between each individual's two responses, and as such the two 
samples (answer 1 , answer 2) are not independent, violating the assumptions of Pearson 
correlation. This also means that the analysis of the effect of age at report suffers from the same 
problem. I suggest using a repeated measures two -way ANOVA design, where you test for the 
interaction effect of age at Tromso4*visit on reported age at menarche. That will tell you if there 
was any significant change in reported age at menarche between Tromso3 and Tromso4, and 
whether age at Tromso4 had an effect on the slope of that change . If this interaction effect is not 
significant, then you can test for the main effect of age at Tromso4 and the main effect of visit. If 
the former is significant, it will tell you that age at report had an effect on reported age at 
menarche across both v isits. If the latter is significant, it will tell you that there was a significant 
change in reported age at menarche between Tromso3 and Tromso4, regardless of age at 
Tromso4. The null hypothesis for each test is that there is no effect (interaction or ma in effect). I 
expect you will fail to reject all null hypotheses, and therefore your overall findings won't 
change, but I think it's important to use an analytical approach that better fits the nature of the 
data.  
 
 
 
 
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.  
 
Unable to assess  
 
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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