The National Center for Health Statistics (NCHS) keeps records of many health-related aspects of people, including the birth weights of all babies born in the United States. The birth weight of a baby is related to its gestation period (the time between conception and birth). For a given gestation period, the birth weights can be approximated by a normal distribution. The means and standard deviations of the birth weights for various gestation periods are shown in the table below. One of the many goals of the NCHS is to reduce the percentage of babies born with low birth weights. The figure below shows the percents of preterm births and low birth weights from 2007 to 2015. 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 lb 1.02 1b 32 to 33 weeks 4.31 1b 0.97 1b Percent of preterm births Percent 34 to 36 weeks 5.74 1b 1.13 lb 8 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 here to search O 72'F Mostly cloudy 9:34 PM