  The simulations of extensive air showers as well as the detectors involved in
their detection play a fundamental role in the study of the high energy cosmic
rays. At the highest energies the detailed simulation of air showers is very
costly in processing time and disk space due to the large number of secondary
particles generated in interactions with the atmosphere, e.g. $\sim 10^{11}$
for $10^{20}$ eV proton shower. Therefore, in order to increase the statistics,
it is quite common to recycle single showers many times to simulate the
detector response. In this work we present a detailed study of the artificial
effects introduced by the multiple use of single air showers for the detector
simulations. In particular, we study the effects introduced by the repetitions
in the kernel density estimators which are frequently used in composition
studies.
