Cognitive Profiles in Preschool Children at Risk for Co-Occurring Dyslexia and ADHD

Round 1

Reviewer 1 Report

The paper describes a comparison between children at cognitive risk of dyslexia and behavioural risk of ADHD and those with only cognitive risk of dyslexia. It is generally well conducted and clear. There is an especially good range of EF tasks used.

As the authors highlight, a lot of previous studies have examined potential causes of the co-occurrence of dyslexia and ADHD. The current study differs from those in that it examines children at risk of those difficulties, prior to formal schooling. I think the authors could make it clearer why this might be a valuable thing to do - for example, that there might be reciprocal causation between early literacy skills and EF. 

The study would be clearer if there was a group of children with only risk of ADHD but not dyslexia.

I think a diagram would be useful to explain the process of allocating individual children to categories.

The authors state in the discussion that it could be that there is a difference between groups in the delay aversion task, but that their study lacks the power to detect it. Effect sizes should be presented throughout to demonstrate the size of group differences.

The discussion states: "As expected, there was no group difference in accuracy or reaction time conflict score on the Flanker test." However they hypothesised deficits in all the EF tasks in the introduction, so this is inconsistent.

Minor issues:

Line 208 I assume the number of females is 571, not 5571.

Line 541 the sentence uses the word 'measure' twice - delete the last 'measurements'.

Author Response

Please see the attachment. Thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

the authors present an exciting study with a large sample size. This are the points I have to make: 

1)      Line 26: The publication of willcut, 2010 is cited not accordingly to the journals style and gives no Information about a comorbity rate between 15-40%. I wonder how the authors concluded that from the study. Plus, as the range is so broad, I recommend citing more than one study here

2)      Line 28ff: You refer here to the definition from the DSM-5, so please state that the definitions are from DSM-5

3)      2.1. Dyslexia à please be careful when reporting that several studies report for an EF deficit in children with dyslexia – did those studies cited control if a comorbid ADHD was present in those children?

4)      Line 73 ff: There are several studies also reporting a deficit on the phonological loop!

5)      My greatest concern and critic is the difference in the nonverbal IQ between the groups. The authors only stated that they did not control for IQ because the IQ differed between the groups. In my opinion, the authors discuss this point far too briefly in the discussion - how could IQ differences have led to differences in the questionnaire scores? One would not expect lower nonverbal IQ scores in a dyslexia-ADHD group. In my opinion, the authors discuss this point far too briefly in the discussion - how could IQ differences have led to differences in the questionnaire scores? One would not expect lower nonverbal IQ scores in a dyslexia-ADHD group. Alternative statistical procedures should be calculated in order to be able to calculate the influence of IQ after all - what about a regression with interaction term, for example? It would also be possible to divide the groups into different IQ sizes, or to use Generalized Linear Models (GLM), which are more flexible and can take into account different distributional assumptions for the error terms. The authors could also set up an ANOVA with IQ as dependent variable to gain more insight about why the IQs differ.

6)      The conclusion needs to be revised. Here, the authors combine both groups and state, that children with dyslexia and adhd have broader cognitive difficulties beyond those directly linked to preliteracy and future reading or spelling problems. This seems obvious, when the group is reported that is at risk for adhd and dyslexia? What are implications for practice? Why is this research important?

Minor editing of English language required

Author Response

Please see the attachment. Thank you.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I am happy with the revision the authos made and have now still the following points: 

Preschool Behaviour Questionnaire (PBQ) [59] : please provide information on the quality criteria of the pbq such as validity and reliability. Please give information about the cut-off criteria of the questionnaire (15 seems to be subclinial – what is a score that is considered clinical)? Why did you choose to take in the top 20% (rather than taking in the first quartile for example)?

In table 1 I am missing descriptive data for the PBQ for all groups (not only the clinical groups). Also in table 1, there is no need for listing male and female numbers, one is sufficient.

I wonder why SES of the mothers was chosen by university degree and not school leaving certificate for example? Is SES between bachelors and masters degree really middle and low or rather both high SES?

In figure 1, there is the information how the groups are divided into adhd and no adhd risk sample is made missing. Also the description of “randomly selected sample” is here misleading or I don’t understand the random selection

Table 4. The NR groups is above expected means in the processing speed index and in the receptive vocabulary score. Please discuss this in the discussion section – were there any were there any upward outliers or are there any other possible explanations?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf