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#statistics

ing status Independent w Genetics, Obstetrics Precise quantification of smoking during pregnancy is difficult in retrospective studies. Routinely collected blood specimens from newborns for screening purposes may provide a low- cost method to objectively measure maternal smoking close to the time of delivery. Serum cotinine is an important bio- marker of recent smoking. A study was performed comparing cotinine levels in dried blood spots in newborns with those in umbilical cord blood (the gold standard) among 428 new- borns in the California Genetic Screening Program (Yang et al. [11]). The lowest detection limit for dried blood spot coti- nine was 3.1 ng/mL. The data in Table 3.9 were presented relating dried blood spot cotinine determinations to umbilical cord blood cotinine determinations. Suppose a cutoff of 25 ng/mL is proposed as a criterion for testing positive based on dried blood spot cotinine levels. 3.64 What is the sensitivity using this cut-point? 3.65 What is the specificity using this cut-point? Suppose it is estimated based on a large sample of births in California that 20% of mothers smoke at the time of delivery. 2 Suppose the screening test for detecting whether a mother smokes at the time of pregnancy is based on a cutoff of 20 ng/mL using dried blood specimens from the newborn. ON X sing dried blood specimens from the newborn. Source: Based on the American Journal of Public Health, 71(12), 1320 1981 E 3.9 Distribution of Cotinine Level in Dried Blood Spots from Newborns by Maternal Active Smoking Status close to the time of delivery among 428 babies delivered in California, 2001-2003 Cotinine Level Matemal in Dried Active Blood (ng/mL) Smoking = yes Materal Active Smoking = no Cotinine Level Maternal in Dried Active Blood (ng/mL) Smoking - yes Maternal Active Smoking - no 9 - 3 2