Most pregnancies are full term, but some are preterm (less than 37 weeks). Of those that are preterm, the Centers for Disease Control and Prevention classifies them as early (less than 34 weeks) and late (34 to 36 weeks). A December 2010 National Vital Statistics Report examined those outcomes in the United States during 2008, broken down by age of the mother. The table shows counts consistent with that report. Is there evidence that the outcomes are not independent of age group?

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Under 20 20 to 29 30 to 39 40 or Over Early Preterm 129 243 165 18 Late Preterm 270 612 424 39 Source: www.cdc.gov/nchs/data/nvsr/nvsr59/nvsr59 01.pdf