[R] bootstrap vs. resampleing

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Hi,

I understand bootstrap can be used to estimate 95%
confidence interval for some statistics, e.g.
variance, median, etc. I have someone suggesting that
by resampling certain proportion of the total samples
(e.g. 80%) without replacement, we can also get the
estimate of confidence intervals. Here we have an
example of 1000 obsevations, we would like to estimate
95% confidence intervals for odds ratio for a
diagnostic test, can I use resampling 80% of the
observations without replacement, instead of
bootstrap, to do this? If not, why is it wrong to do
it this way?

Thanks