# Problem 9,  STAT 789,  Summer 2006
# Jackknife estimates of bias and standard error for Pr. 11.12 of E&T.  

LSAT <- c(576,635,558,578,666,580,555,661,651,605,653,575,545,572,594) 
GPA <- c(3.39,3.30,2.81,3.03,3.44,3.07,3.00,3.43,3.36,3.13,3.12,2.74,2.76,2.88,2.96) 

corr.hat <- cor( LSAT, GPA )

corr.hat.rep <- numeric()
for (i in 1:15) corr.hat.rep[i] <- cor( LSAT[-i], GPA[-i] )

# jackknife estimate of bias:
14*( mean( corr.hat.rep ) - corr.hat )

# jackknife estimate of standard error:
sd( corr.hat.rep )*14/sqrt(15)