1. Bootstrap resampling methods: something for nothing?
Gary L Grunkemeier, PhD, YingXing Wu, MD 
The Annals of Thoracic Surgery 
Volume 77, Issue 4, Pages (April 2004)
DOI: /j.athoracsur

2. Fig 1
Simulation (random draws) from a population can reproduce the original distribution exactly, if enough draws are made. With increasing sample size, simulations from a standard normal distribution can approximate the underlying distribution to whatever accuracy is desired.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )

3. Fig 2
Bootstrap confidence intervals for the observed-to-expected (O/E) ratio. Five intervals were produced for each of four increasing number of bootstrap samples (B). As B increases, the different iterations converge to the same size intervals, within as close a tolerance as desired. The solid horizontal line represents O/E = 1, or observed = expected. All of the confidence intervals include this line, so there is no evidence of mortality different than expected. The dashed horizontal lines represent the interval computed from the usual normal approximation formula.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )