Psychologists concerned about self-injurious behaviors (e.g., smoking, eating fatty diets, drug abuse, etc.) worry about the effects of maternal smoking on the incidence of low birth weight babies, who are known to be at risk for developmental problems. The Centers for Disease Control and Prevention has published statistics relating maternal smoking to low birth weight.

The data follow in terms of the percentage of birth weights < 2,500 grams. Find a way to present these data that illustrates this relationship clearly. Why is this relationship not likely to be a statistical fluke?