Consider the linear model y $=$ X$+.$ Let X$($i$)$ denote the X matrix with the ith row X'deleted. Without loss of generality, we can partition X as X $(6)$ X $=3$ x so we can write X$\text{'}$X $=$ XY$,$ X$(1)+$ Xia', or X$,$X$(0)=$ X$\text{'}$X $2$;$2.$ Verify the formula $($X$\text{'}$X$)-?$xx$($X$\text{'}$X$)-1($X$()$ X$($i$))1=($X$\text{'}$X$)-1+1$ hii where hii $=$ x;$($X$\text{'}$X$)-1$x; is the ith diagonal element of the hat matrix. Note: This formula is the main result used to relate regression estimates with and without the ith case so that we do not need to calculate estimates from n separate regressions.