Create a new variable (pwk) that classifies each birth according to person-weeks at risk. Assign term births the value pwk = 17, the maximum number of person-weeks at risk for preterm birth. For preterm births, assume that the birth occurred half-way through the week in which it occurred. For example, a birth that occurred during the 21st week of gestation (weeks of gestation completed = 20) would be assigned pwk = 0.5, a birth during the 22nd week (weeks = 21) would be assigned pwk = 1.5, and a birth during the 37th week (weeks = 36) would be assigned pwk = 16.5. Document the new variable, confirm it was coded as intended, assess whether your coding strategy conforms to the instructions, and assign a meaningful label to the variable