A Recent Issue of the New England Journal of Medicine

Multiple Choice

A recent issue of the New England Journal of Medicine reports a study of all 122,754 infants born over an 8.5-year period at Parkland Hospital in Dallas, leaving out multiple births and infants with birth defects. The researchers wanted to know if there is a specific birth weight below which infant death and illness increases sharply.
This study is a(n)

A) randomized comparative experiment.
B) experiment, but subjects are not assigned at random.
C) probability sample of a population.
D) observational study, but not a probability sample.
E) stratified sample.