Number of births per day in USA from 1969-01-01 to 1988-12-31.
Data source: National Vital Statistics System natality data, as
provided by Google BigQuery and exported to cvs by Chris Mulligan (sum
data http://chmullig.com/wp-content/uploads/2012/06/births.csv) and
Robert Kern (whole time series
http://www.mechanicalkern.com/static/birthdates-1968-1988.csv).

Data columns
- year
- month
- day
- births
- day_of_year
- day_of_week
- id
- day_of_year2 = this is same as day_of_year
