It is well-documented that active maternal smoking during pregnancy is associated with lower-birth-weight babies. Researchers Fernando D. Martinez and associates wanted to determine if there is a relationship between paternal smoking habits and birth weight. The researchers administered a questionnaire to each parent of newborn infants. One question asked whether the individual smoked regularly. Because the survey was administered within 15 days of birth, it was assumed that any regular smokers were also regular smokers during pregnancy. Birth weights for the babies (in grams) of nonsmoking mothers were obtained and divided into two groups, nonsmoking fathers and smoking fathers. The given data on the next page are representative of the data collected by the researchers. The researchers concluded that the birth weight of babies whose father smoked was less than the birth weight of babies whose father did not smoke.

(a) Is this an observational study or a designed experiment? Why?
(b) What is the explanatory variable? What is the response variable?
(c) Can you think of any lurking variables that may affect the results of the study?
(d) In the article, the researchers stated that "birthweights were adjusted for possible confounders ...." What does this mean?
(e) Determine summary statistics (mean, median, standard deviation, quartiles) for each group.
(f) Interpret the first quartile for both the nonsmoker and smoker group.
(g) Draw a side-by-side boxplot of the data. Does the side-by-side boxplot confirm the conclusions of the study?

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4194 3062 3544 4054 4248 3128 3471 3994 3732 3436 Nonsmokers 3522 3771 3746 3518 3719 3290 4354 2976 3823 3976 3454 3998 3783 3150 4019 4216 3884 3493 3668 2860 3423 3686 3544 3807 4067 3963 3302 3769 3263 4131 Smokers 3455 2986 3502 3255 3282 2851 3548 3892 3509 3129 3066 2918 3457 3234 2746 3145 4104 2768 3629 4263 3