Gender Differences in the Comorbidity of ADHD Symptoms and Specific Learning Disorders in a Population-Based Sample

Round 1

Reviewer 1 Report

The paper deals with an important and interesting topic. It is a current and relevant issue in these pandemic times.

Author Response

#We would like to thank the reviewer for taking the time to read our manuscript and giving such positive feedback. A native speaker did proof-read the revised version of the manuscript.

Reviewer 2 Report

The article describes a study investigating gender differences of co-occuring learning disorders in children with and without ADHD. The topic is of high interest, however, there are several issues that should be addressed. 

1. The ADHD diagnosis was not a clinical diagnosis but solely based on questionnaires filled out online. Therefore throughout the whole manuscript the children should not be termed as "ADHD" but as "children with increased ADHD symptoms".
2. Same goes for learning disorders. 
3. Is there information on how many of the children had a previous ADHD diagnosis? 
4. Is there information about medication with stimulants or other psychopharmacological and non-psychopharmacological treatment? 
5. Has an ethics committee approved of the study? 
6. Is there any information about cultural backgound? Multilingual children? German not the mother tongue? Parents with migration background? All influencing factors on reading abilities and should be taken into account.  
7. Table 1; it would be more enlightning to add the p-values for differences between boys and girls/age groups 
8. As this is a scientific article, I would suggest to use the medical terms for the disorders, e.g. dyscalculia (instead of "math disorder") and dyslexia (instead of "reading disorder") and so on. And be precise if the full diagnosis of a dyscalculia is meant or really just difficulties and worse performance in maths etc. with regards to the previous studies that were described and cited. Also, the same terms should be used consistendly, in the main text it is mostly "math disorder" but in Figure 2 it is "arithmetic disorder". 
9. It is not really clear how it was confirmed that this sample was representative for the German general population in 2017. The authors state as limitation that higher educated mothers were over represented but what about the general demographics? 
10. It is not very clear how the sample was recruited, please give more details?
11. Any information about ADHD or other mental disorder diagnosis in the parents? 
12. What is the hypothesis that girls in general have more difficulties in math?

The English needs extensive revision by a native speaker. 

Author Response

#We would like to thank the reviewer for taking the time to give us this extensive and helpful feedback. We integrated all comments in the updated version of the manuscript and reply in more detail below.

1. The ADHD diagnosis was not a clinical diagnosis but solely based on questionnaires filled out online. Therefore throughout the whole manuscript the children should not be termed as "ADHD" but as "children with increased ADHD symptoms".

#1 We used the term ADHD to clarify the categorical nature of most of our analyses. However, we indeed did not use clinical diagnostic categories and therefore we changed the term consistently from “ADHD” to “ADHD symptoms” or “increased ADHD symptoms” throughout the whole manuscript (except when referring to studies with clinical samples).

2. Same goes for learning disorders. 

#2 Learning disorders were diagnosed in accordance with the German S3 guideline for clinical diagnoses for reading and spelling disorders (Evidenz-und konsensbasierte Leitlinie (S3); AWMF-Registernummer 028 -044; https://www.kjp.med.uni-muenchen.de/download/leitlinie_lrs_kjp_langfassung.pdf

) as well as math disorder (Evidenz-und konsensbasierte Leitlinie (S3); AWMF-Registernummer 028 – 046; https://www.awmf.org/uploads/tx_szleitlinien/028-046l_S3_Rechenst%C3%B6rung-2018-03_1.pdf) using the standardized tests that are typically used (and named in the S3 Guidline) with a  performance > 1 SD below the mean, exclusion of children with IQ ≥ 70, and exclusion of children with visual impairment, hearing impairment or neurological disease. Therefore, we would prefer to use “learning disorders” and hope that the reviewer agrees.

3. Is there information on how many of the children had a previous ADHD diagnosis? 

#3 The parental questionnaire included the items: “Are/were there any psychiatric/neurological diagnoses?” “Which psychiatric/neurological diagnoses are/were there?" (German: Gibt/gab es eine psychiatrische/neurologische Diagnose? Welche psychiatrische/neurologische Diagnose gibt/gab es? (Mehrfachauswahl möglich) From the drop down menu among other options parents were able to select the option “attention-deficit/hyperactivity disorder” (German: “Aufmerksamkeitsdefizit-/Hyperaktivitätsstörung”). However, we found that the agreement of our categorization and the parents declaration in these items were almost by chance:

These deviations could be due to (1) the intermixture of past (were) and present (are) in the same question and (2) successfully treated children, that might not show symptoms above the cut off in the ADHD questionnaire. Therefore, we did not include this information in the manuscript.

4. Is there information about medication with stimulants or other psychopharmacological and non-psychopharmacological treatment? 

 #4 The parental questionnaire included the items: “Does your child currently take medication?” “Which medication?" (German: Nimmt Ihr Kind aktuell Medikamente ein? / Welche Medikamente nimmt Ihr Kind aktuell ein?)

The open-end answers for the question „Which medication?” were categorized into various categories, of which one was “ADHD medication” (German: “ADHS-Präparat”). However, only one of the 3020 parents indicated that the child used ADHD medication. Therefore, we did not find this information helpful for the interpretation of our hypotheses and did not include it in the manuscript. Asking for names of medications (e.g., Riatlin, Medikinet etc.) would have been more precise, but was not included due to the already very extensive parental questionnaire.

5. Has an ethics committee approved of the study? 

#5 We are sorry for not including this information. We now report: “The study was approved by the ethics committees of the University Hospital of the Ludwig-Maximilians-University Munich and the DIPF | Leibniz Institute for Research and Information in Education, Frankfurt am Main.“

6. Is there any information about cultural backgound? Multilingual children? German not the mother tongue? Parents with migration background? All influencing factors on reading abilities and should be taken into account.  

#6 The following Items were part of the parental questionnaire:

1. Did you migrate from another country? (Sind Sie aus einem anderen Land eingewandert?)
2. In which year did you migrate to Germany? (In welchem Jahr sind Sie nach Deutschland eingewandert?)
3. Was your child born in Germany? (Ist Ihr Kind in Deutschland geboren?)
4. Since how many years do you live in Germany? (Seit wie vielen Jahren lebt Ihr Kind in Deutschland?)
5. Is German the mother tongue (dominant language) of your child? (Ist Deutsch die Muttersprache (dominante Sprache) Ihres Kindes?)
6. What is the mother tongue of your child? (Was ist die Muttersprache Ihres Kindes?)
7. Does your child grow up multilingual? (Wächst Ihr Kind mehrsprachig auf?)
8. With which languages does your child grow up? (Mit welchen Sprachen wächst Ihr Kind auf?)
9. Do you speak any other languages at home? (Werden noch andere Sprachen zu Hause gesprochen?)
10. Which other languages do you use at home? (Welche anderen Sprachen werden zu Hause noch gesprochen?)
11. Nationality of the child (Nationalität des Kindes)

The cultural and linguistic background of a child could have an influence on the learning abilities of a child. As the table below shows, the proportion of children with a learning disorder was a bit higher in the group of children with a non-German mother tongue (based on question 5).

As we did not have information about the linguistic abilities of the children, we were not able to judge to what extent the different mother tongue has played a role in the below-average learning scores. We decided not to exclude these children, because that would have made the sample less representative for the German population (a significant proportion of children in German schools have a non-German mother tongue). Also, it is not that unlikely that the categorization of these children as having a learning disorder is correct, especially since the tests used for assessing spelling (WRT 3+ and 4+) and math (Cody) have shown to be measurement invariance with respect to non-German mother tongue. We did, however, add information about the nationality and mother tongue (German, yes or no) of the children to the method section, to improve the sample description.

We also added this section to the discussion, to point to the importance of dominant language in this context:

“Lastly, our study is merely descriptive. We did not focus on causes for gender-specific associations of ADHD symptoms and learning difficulties in reading, spelling and math. To be able to take preventive steps before children develop learning difficulties, future studies should focus on the factors causing gender-specific associations between ADHD symptoms and learning difficulties (e.g., other dominant language or psychological problems of the parents).”

7. Table 1; it would be more enlightning to add the p-values for differences between boys and girls/age groups 

#7 Thank you for this helpful remark, we added the p-values to the table.

8. As this is a scientific article, I would suggest to use the medical terms for the disorders, e.g. dyscalculia (instead of "math disorder") and dyslexia (instead of "reading disorder") and so on. And be precise if the full diagnosis of a dyscalculia is meant or really just difficulties and worse performance in maths etc. with regards to the previous studies that were described and cited. Also, the same terms should be used consistendly, in the main text it is mostly "math disorder" but in Figure 2 it is "arithmetic disorder". 

#8 In accordance with the ICD-10 (the classification system that is used in the German health care system) we would prefer to use the terms reading and math disorder and hope the reviewer agrees. We also adapted Figure 2.

9. It is not really clear how it was confirmed that this sample was representative for the German general population in 2017. The authors state as limitation that higher educated mothers were over represented but what about the general demographics? 

#9 The representativeness of the sample has already been described in a previous publication (Visser et al., 2020). Therefore, we do not discuss it in detail here, but we have added the following sentence to the paragraph 2.1 (Participants and Procedure):

“For more detailed information about the representativeness of the sample, we refer to Visser et al. (2020).”

Furthermore, we added a more detailed paragraph about the recruitment (see also reply #10), which includes the following information:

“The families were chosen randomly so that the sample would be representative of the population in terms of gender and age (8.8–10.8 years; Bavaria) or grade (Hesse).”

10. It is not very clear how the sample was recruited, please give more details?

#10 We now added these more detailed descriptions: “We invited families with children in grade 3 and/or grade 4 in the two German federal states of Hesse (through the Hessian Ministry of Culture; n = 25,000) and Bavaria (addresses provided by local registration offices; n = 27,734) to participate in this study. The families were chosen randomly so that the sample would be representative of the population in terms of gender and age (8.8–10.8 years; Bavaria) or grade (Hesse).

The invitation letter contained instructions and login data for the application (app), which could be downloaded onto a tablet or smartphone to provide information on and to assess the academic skills and psychopathological profile of the children within eight weeks. In total, 4,542 families logged into the app. ”

11. Any information about ADHD or other mental disorder diagnosis in the parents? 

#11 The following items were part of the parental questionnaire:

1. Are/were there any reading or writing disorders in your family? (Gibt/gab es in der Familie Lese-/Rechtschreibstörungen?)
2. How is the person affected related to your child? (Wie ist der/die Betroffene mit Ihrem Kind verwandt?)
3. Are/were there any math disorders in your family? (Gibt/gab es in der Familie Rechenstörungen?)
4. How is the person affected related to your child? (Wie ist der/die Betroffene mit Ihrem Kind verwandt?)
5. Are/were there any attention disorders in your family? (Gibt/gab es in der Familie Aufmerksamkeits-/Konzentrationsstörungen?)
6. How is the person affected related to your child? (Wie ist der/die Betroffene mit Ihrem Kind verwandt?)
7. Are/were there any psychological strains in your family (e.g., depression, anxiety)? (Gibt/gab es in der Familie psychische Belastungen (z.B. Depression, Ängste)?)
8. How is the person affected related to your child? (Wie ist der/die Betroffene mit Ihrem Kind verwandt?)

As discussed in reply #6 we make no statements about the cause of learning difficulties in children with ADHD and about gender specific causes. Therefore, we did not include these infos in the article. We think that due to the cross-sectional design of our study we cannot assess cause and effect in a valid way. However, we do agree that mental disorders of the parents could be an important factor that influences the development of learning difficulties and might be a cause for gender-specific associations of ADHD symptoms and learning difficulties. Therefore, we included the following paragraph in the discussion:

“Lastly, our study is merely descriptive. We did not focus on causes for gender-specific associations of ADHD symptoms and learning difficulties in reading, spelling and math. To be able to take preventive steps before children develop learning difficulties, future studies should focus on the factors causing gender-specific associations between ADHD symptoms and learning difficulties (e.g., other dominant language or psychological problems of the parents).”

12. What is the hypothesis that girls in general have more difficulties in math?

#12 Since we focused on gender differences in children with and without increased levels of ADHD symptoms we did not test the hypothesis that girls in general have more learning difficulties in math. However, previous literature points in that direction (Moll et al., 2014) and we discuss this: “In our sample, girls without ADHD symptoms also had a higher rate of math disorders (16.6%) than boys without ADHD symptoms (11.8%), which is in line with previous studies [30]“. We also discuss that the increase in probability to have math difficulties when having ADHD symptoms is higher in girls (2.5 fold) than boys (2 fold). To keep the manuscript focused on our ADHD specific research questions we did not test gender differences in children without ADHD symptoms.

The English needs extensive revision by a native speaker. 

# A native speaker did proof-read the revised version of the manuscript.

References

Moll, K., Kunze, S., Neuhoff, N., Bruder, J., & Schulte-Körne, G. (2014). Specific learning disorder: Prevalence and gender differences. PLoS ONE, 9(7). https://doi.org/10.1371/journal.pone.0103537

Visser, L., Kalmar, J., Linkersdörfer, J., Görgen, R., Rothe, J., Hasselhorn, M., & Schulte-Körne, G. (2020). Comorbidities between specific learning disorders and psychopathology in elementary school children in Germany. Frontiers in Psychiatry, 11, 292. https://doi.org/10.3389/fpsyt.2020.00292

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Manuscript has improved, no further comments. 

Author Response

Thank you very much for your suggestion