From the Exploring Data website - http://curriculum.qed.qld.gov.au/kla/eda/
© Education Queensland, 1997

The 1970 Draft Lottery

Source: Data and Story Library

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 the trend is not at all clear when viewed as 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.

For more detailed information about this most interesting dataset I recommend you read the article Nonrandom Risk: The 1970 Draft Lottery from volume 5 of the Journal of Statistics Education.

The datasets for both the 1970 draft and the 1971 draft (for comparison purposes) are available in NCSS, Excel 4.0 and tab-delimited format from the Datasets page.