A new study suggests that women with asthma exposed to air pollution, even befor

Question

A new study suggests that women with asthma exposed to air pollution, even before conception, significantly increase their risk of delivering a premature baby. The researcher reported gestational ages for two groups of women with asthma – one group of 43 women exposed to air pollution (mean = 34 weeks with a standard deviation of 1 week) and another group of 46 women not exposed to air pollution (mean = 40 weeks with a standard deviation of 1 week). Which one of the following statements is INCORRECT? (Set alpha level at 0.05; Pooled standard deviation = 1)

A. The null hypothesis is that gestational age is not different between women with asthma who are exposed to air pollution and those who are not exposed to air pollution.

Explanation / Answer

n1 = 43
n2 = 46
x1bar = 34.0000
x2bar = 40.0000
sigma1 (s1) = 1.0000
sigma2 (s2) = 1.0000

Sp = sqrt(((n1-1)*s1^2+(n2-1)*s2^2)/(n1+n2-2))
= sqrt(((43 -1) * 1 + (46-1) *1)/(43+46-2))
= 1

x1bar - x2bar = -6.00
SE = 1.0000
CI = 95%
DF = n1+n2-2 = 87

z = (x1 -x2) /Sp *sqrt (1/n1 +1/n2)
= -6/1 *sqrt(1/43+1/46)
= -28.29

Incorrect answers is
C. The degrees of freedom is 88.

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