cont2 <- function()
{
year <- round(runif(1,1980,2012))
mark <- drawMarker()
ex <- drawExp("beneficial")
n1 <- round(runif(1,5,100))
n2 <- round(runif(1,5,100))
d <- runif(1,0,1)
m <- c(mark$m,round(mark$m+d*mark$SD,1))
conf.level <- sample(c(.8,.9,.95,.95,.95,.95),1)
writeLines(strwrap(paste("A ",year," study investigated whether ",ex$act," may lower ",mark$marker," levels. The study obtained a sample of ",n2," individuals who do not ",ex$action," and ",n1," individuals who do. They found that among the individuals who ",ex$action,", their average ",mark$marker," levels were ",m[1],", while the control group had an average of ",m[2],". The pooled standard deviation was ",mark$SD,".",sep="")))
writeLines(strwrap(paste("a) What is the probability that the difference between the two groups would be as great or greater than what the study observed, if ",ex$act," truly has no effect on ",mark$marker," levels?",sep="")))
writeLines(strwrap(paste("b) Provide a ",100*conf.level,"% confidence interval for the amount by which ",ex$act," reduces ",mark$marker," levels.",sep="")))
cat("\n\n")
readline("Press <Enter> to reveal answers")
cat("\n\n")
d <- m[2]-m[1]
SE <- mark$SD*sqrt(1/n1+1/n2)
p <- 2*pt(-d/SE,n1+n2-2)
if (p < .001) p <- "< 0.001"
else p <- paste("= ",round(p,3))
cat("a) p ",p," (two-sample Student's t-test)\n",sep="")
alpha <- 1-conf.level
l <- d+qt(alpha/2,n1+n2-2)*SE
u <- d-qt(alpha/2,n1+n2-2)*SE
cat("b) CI = (",round(l,2),", ",round(u,2),") (CI for a difference of two means)\n",sep="")
}
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