An examination of the histogram shows significant seasonal variations. The months July - October show higher than expected births and March - May show the most significant decline in births. Perhaps the most reasonable explanation is that conceptions are up in the months of October through January and down in June through August. You be the judge.
Wonder if HN has an explanation as to why :)
It would be interesting to see if the trend is reversed in the Southern Hemisphere, although you'd be hard pressed to find anywhere that gets as cold in the winter as North America does that has a similar wealth as North America.
But, yeah, I agree :)
I wonder if this has changed in more recent years with changes in demographics.
