# Two means, independent (and large) samples.
# Birth weights, babies with smoker vs nonsmoker mothers.
xb1=6.78  # smoker
s1=1.43
n1=50

xb2=7.18  # nonsmoker
s2=1.60
n2=100

# 95% CI for mu2-mu1
me=1.96*sqrt(s1^2/n1+s2^2/n2)
xb2-xb1-me
xb2-xb1+me

# Hypothesis test of Ho: mu2-mu1=0  vs  Ha: mu2-mu1>0
z=(xb2-xb1-0)/sqrt(s1^2/n1+s2^2/n2)
p=1-pnorm(z)
z
p