# R scripts for means, one and two sample.


# One mean, small sample t test.
# Example is mercury concentrations in a lake (mg/m^3).

mu0=1.2   # Baseline before mercury spill.
alpha=.05  # Test significance level.
x=c(1.60,1.77,1.61,1.08,1.07,1.79,1.34,1.07,1.45,1.59,1.43,
    2.07,1.16,.85,2.11)   # Measurements after spill.

t.test(x,mu=mu0,conf.level=(1-alpha))

boxplot(x)
abline(h=mu0,lty=2)


# Paired data example, textbook prices at UCLA vs Amazon
texts=read.table("textbooks.txt",header=TRUE)
attach(texts)
diff=uclaNew-amazNew
diff
mu0=0
alpha=.05
t.test(diff,mu=mu0,conf.level=(1-alpha))

# Alternative.
# t.test(uclaNew,amazNew,paired=TRUE,mu=mu0,conf.level=(1-alpha))

boxplot(diff)
abline(h=mu0,lty=2)

detach(texts)


# Two sample t test.  Example is androsterone levels in
# heterosexual (s) and homosexual (g) males, from
# Margolese, MS 1970.  Homosexuality: a new endocrine
# correlate.  Hormones and Behavior 1:151-155.  By default
# the variances are assumed unequal and the
# Welch-Satterthwaite approximation is used.

andro=read.table("androsterone.txt",header=TRUE)
attach(andro)
andro

t.test(androsterone~orientation,mu=0,conf.level=.95)

boxplot(androsterone~orientation,range=0,
  names=c("gay","straight"),ylab="androsterone",boxwex=.5)

# Alternative.
# andro.g=androsterone[,orientation=="g"]
# andro.s=androsterone[,orientation=="s"]
# t.test(andro.g,andro.s,mu=0,conf.level=.95)

detach(andro)