This is the email I've sent to Dr Colen. Will let you know if there's a reply.

Could you email me a copy of your study re siblings breast of bottle fed? It was an interesting idea, and may provide some useful data for the book I am completing. 

As I read the press release, you were looking at outcomes in 
children born between 1957 and 1965 (the 1979 cohort), 
and their children, whose birthdates had to fall somewhere  between 1968-1982 (if 14 and 4year olds in the 1986 cohort) 
or at latest 2006 (if there were 4 year olds in the 2010 cohort.)

I hope the article specifies the years of birth and ages of children; if it does not, can you provide a summary? Also details of how many first and second generation children were in the study?

And does the study connect the infant feeding data, so that we know whether  the mothers of second generation children were themselves the bottle-fed or the breastfed? There would then be four groups of children (breastfed by breastfed mother, breastfed by bottle-fed mother, bottle-fed by breastfed mother, bottle-fed by bottle-fed mother) in the analysis  of the second generation 1986-2010 cohorts. Does the data even permit you to do this? 

This is particularly important as many things changed in the time frame 1957-2006, as you might realise.  What is true at one time and location is quite different at another. The intergenerational effects of infant feeding have the potential to support a null hypothesis if, as expected over that time frame, the social class of breastfeeding mothers shifted dramatically, from the disadvantaged in the 1950s-1960s. (Not only the social class of mothers breastfeeding, but also the infant formulas in use, which were very different by 1990 than in 1960.) The existing evidence for epigenetic changes - such as differences in reproductive tissue development and chromosomal damage- needs to be factored into any analysis. 

Looking forward to reading the paper in full...
> 
> ---------------------------------------------------------------------
> 
> Date:    Wed, 26 Feb 2014 18:42:48 +0100
> From:    heather <[log in to unmask]>
> Subject: Re: study includes siblings
> 
>> I looked at this a while ago Heather. From memory it suffers from 
>> comparing never vs ever breastfed (it's quite a difficult paper to 
>> read and the methods are not very clear). And they selectively cite 
>> from the PROBIT study.
>> Karleen Gribble
>> Australia
> 
> 
> Thanks, Karleen, but it is a newly published study, apparently, and 
> the (not very clear) article I linked to states "For each sample, the 
> researchers sought answers to two basic questions: Was at least one 
> child breast-fed and, if so, what was the duration of breast-feeding?"
> 
> The researchers looked at children aged 4 to 14 years old and some of 
> the measures examined included aspects which you would not really 
> expect bf to have a measurable impact - hyperactivity and digit 
> recognition???
> 
> Some of the report is hard to understand:
> 
> "Some examples of differing benefits: Breast-feeding's beneficial 
> influence on BMI decreased by 66 percent between siblings across 
> families and siblings within families. The magnitude of the 
> beneficial effects of breast-feeding for math, reading, vocabulary 
> and intelligence declined by between 69 and 29 percent, respectively, 
> when comparing data across families to data from within families."
> 
> Er...well, that's as clear as mud:( :( ....but if bf makes a 29 per 
> cent difference (whatever that means....) between siblings,  then 
> that's pretty significant, isn't it?
> 
> (A kind lactetter has just forwarded me the whole paper so I will 
> look at it properly)
> 
> Heather Welford Neil
> NCT bfc, tutor, UK
> -- 
> 
>             ***********************************************


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