In my literature book I found that the z-score can be calculated by the following function:
z = (data point - mean) / standard deviation
Now I'm reading on bootstrap and I found that they calculated the z-score using the outcome of the boostrap analysis by the following R code:
$tm$ is a vector holding the difference in response times between two groups.
$diff.mean = function(x,i)$ $mean(x[i])$
$boot(tm,diff.mean,R=20000)$ $$ z = tm.boot$t0/sd(tm.boot$t) $$ Can someone explain why the mean is not used in this formula? Is it because the mean is 0? If so, why is the mean 0?