(downloaded from DASL)
Story Name: Draft Lottery 1970
Story Topics: Government
Datafile Name: Draft Lottery
Methods: Boxplot , Correlation , Scatterlots , Smoothing
Abstract: In 1970, Congress instituted a random selection process
for the military draft. All 366 possible birth dates were placed in plastic
capsules in a rotating drum and were selected one by one. The first date
drawn from the drum received draft number one and eligible men born on
that date were drafted first. In a truly random lottery there should be
no relationship between the date and the draft number. However, this dataset
suggests that men born later in the year were more likely to be drafted.
While it is impossible to view this trend in a scatterplot of draft
number vs. birth date, a series of side-by-side boxplots by month illustrate
it clearly. The correlation between draft number and birth date is -0.226,
which is significantly different from zero. A further investigation of
the lottery revealed that the birthdates were placed in the drum by month
and were not thoroughly mixed.
Alternatively, drawing a smoothed curve through the points also shows
the pattern of decreasing priority values in the end months of the year
which was not apparent in the original scatterplot. The smoothed curve
here uses the lowess method.
Image: Scatterplot of draft selection number by day of year
Image: Side-by-side boxplots of draft selection number by month
Image: Scatterplot of draft selection number by day of year,
with smoothed lowess curve.
