Gestation Mean birth Standard 12- period weight deviation Preterm = under 37 weeks 11 - Low birth weight = under 5.5 pounds Under 28 weeks 1.60 1b 0.76 1b 10 28 to 31 weeks 3.20 1b 1.02 1b 32 to 33 weeks 4,31 1b 0.97 1b 9 Percent of preterm births Percent 34 to 36 weeks 5.74 1b 1.13 lb 37 to 38 weeks 6.92 1b 1.07 1b Percent of low birth weights 39 to 40 weeks 7.60 1b 0.99 1b 41 weeks 8.00 1b 0.99 1b 2007 2008 2009 2010 2011 2012 2013 2014 2015 42 weeks and over 8.16 1b 1.12 1b Year EXERCISES 1. The distributions of birth weights for three 2. What percent of the babies born within each gestation periods are shown, Match each curve gestation period have a low birth weight (under with a gestation period. Explain your reasoning. 5.5 pounds)? (a) (a) 28 to 31 weeks (b) 32 to 33 weeks (c) 39 to 40 weeks (d) 42 weeks and over 3. Describe the weights of the top 10% of the babies born within each gestation period. Pounds (a) Under 28 weeks (b) 34 to 36 weeks (b ) (c) 41 weeks (d) 42 weeks and over 4. For each gestation period, what is the probability that a baby will weigh between 6 and 9 pounds at birth? (a) Under 28 weeks (b) 32 to 33 weeks Pounds (c) 37 to 38 weeks (d) 41 weeks (c) 5. A birth weight of less than 3.25 pounds is classified by the NCHS as a "very low birth weight." What is the probability that a baby has a very low birth weight for each gestation period? (a) Under 28 weeks (b) 28 to 31 weeks Pounds (c) 32 to 33 weeks (d) 39 to 40 weeks 260 CHAPTER 5 Normal Probability Distributions