It could be the seasonal use of pesticides, as this study suggests, or it could be seasonality in nutrition of mothers and infants, or seasonality of environmental stressors, or seasonality of mothers' hormone profiles. Most likely all or most of these and other factors play a role, and the relative importance of the factors differs between geographic regions, between socioeconomic strata, and between times in history.
But there is one factor that has been repeatedly demonstrated to play no role at all: the position of planets, moons and stars, as seen from Earth, at the moment of birth of a baby....
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The news article says nothing about how they determined the month of conception. With an n = 1,667,391, I suspect that they simply subtracted 9 months from the date of birth, which does nothing to account for premature or post-term babies.
There's nothing to account for the nutrition of the mothers, who would be going through much of the most sensitive time for fetal development during the late fall and winter months, with less available fresh produce.
And, since presumably all of these kids would be starting school in August/September, obviously some would be less mature when first starting school.
Too many unaccounted for possibilities for this study to have much, if any, significance, IMHO.
Also, with an N that big they have a huge amount of power, aren't they guaranteed to find significance? What are the effect sizes for these differences in test scores? Ice Cream sales are also highest June through August so is not just as likely that too much lactose is causing our children to be mathematical morons?
I remember a similar study from Texas a couple of years ago. I know I blogged about it in detail (using some of the same arguments as the two of you presented), but now I cannot find the post! Perhaps it was on some forum before I even started a blog - I do not remember.
WTF? Where is peer review when you need it?
Nitrates? Pesticides? Summer brings about far more changes that could be just as easily responsible. What about increased solar radiation? Easier access to more fresh fruit? More flea and tick bites? Switching from bourbon to gin and tonic (or is that just me)?
Touting findings that are presented at a meeting, instead of waiting until they have been reviewed and published, is the lowest form of huckesterism.
And we blogger about a study with similar problems quite < ahref="http://scienceblogs.com/clock/2007/02/seasonality_of_preterm_births.php">recently.
Right--I think it's the summer reruns on TV.
I suspect that chezjake is on it better - most schools have 'cut off birthdays' in August. Kids in the same class born in August can be 11 months younger than kids considered their peers. Not a big deal for a geezer like Bora or myself, but a large difference when you are 7!