xbar1=1500
s1=100
n1=7
xbar2=1300
s2=80
n2=13
nu=(s1^2/n1+s2^2/n2)^2/((s1^2/n1)^2/(n1-1)+(s2^2/n2)^2/(n2-1))
xbar1-xbar2+c(-1,1)*qt(1-a/2,df=nu)*sqrt(s1^2/n1+s2^2/n2)
nu
xbar1=1500
s1=100
n1=7
xbar2=1300
s2=80
n2=13
nu=(s1^2/n1+s2^2/n2)^2/((s1^2/n1)^2/(n1-1)+(s2^2/n2)^2/(n2-1))
xbar1-xbar2+c(-1,1)*qt(1-a/2,df=floor(nu))*sqrt(s1^2/n1+s2^2/n2)
xbar1=1500
s1=100
n1=7
xbar2=1300
s2=80
n2=13
nu=(s1^2/n1+s2^2/n2)^2/((s1^2/n1)^2/(n1-1)+(s2^2/n2)^2/(n2-1))
xbar1-xbar2+c(-1,1)*qt(1-a/2,df=10)*sqrt(s1^2/n1+s2^2/n2)
xbar1=1500
s1=100
n1=7
xbar2=1300
s2=80
n2=13
nu=(s1^2/n1+s2^2/n2)^2/((s1^2/n1)^2/(n1-1)+(s2^2/n2)^2/(n2-1))
xbar1-xbar2+c(-1,1)*qt(1-a/2,df=6)*sqrt(s1^2/n1+s2^2/n2)
xbar1-xbar2+c(-1,1)*qt(1-a,df=6)*sqrt(s1^2/n1+s2^2/n2)
xbar1-xbar2-qt(1-a,df=6)*sqrt(s1^2/n1+s2^2/n2)
xbar1-xbar2-qt(1-a,df=10)*sqrt(s1^2/n1+s2^2/n2)
xbar1-xbar2+qt(1-a,df=10)*sqrt(s1^2/n1+s2^2/n2)
xbar1-xbar2+qt(a,df=10)*sqrt(s1^2/n1+s2^2/n2)
x1=190
n1=300
phat1=x1/n1
phat1
x2=228
n2=400
phat2=x2/n2
phat2
phat1-phat2+c(-1,1)*qnorm(0.975)*sqrt(phat1*(1-phat1)/n1+phat2*(1-phat2)/n2)
x=rnorm(7,1500,100)
x
y=rnorm(13,1200,80)
y
summary(x)
summary(y)
t.test(x,y)
s1=sd(x)
s2=sd(y)
n1=length(x)
n2=length(y)
(s1^2/n1+s2^2/n2)^2/((s1^2/n1)^2/(n1-1)+(s2^2/n2)^2/(n2-1))
?t.test
t.test(x,y,alternative="less",conf.level=0.99)
t.test(x,y,alternative="greater",conf.level=0.99)
(1200-1300)/(150/sqrt(7))
qt(0.01,6)
savehistory("N:/321_su19_data/20190617_in_class.Rhistory")