  A large population of z>5 Lyman break galaxies has been identified in recent
years. However, the high redshift galaxies selected by different surveys are
subject to a variety of selection effects - some overt, others more subtle. We
present an analysis of sample completeness and contamination issues in high
redshift surveys, focusing on surveys at z=5 and using a
spectroscopically-confirmed low redshift sample from the DEEP2 survey in order
to characterise contaminant galaxies. We find that most surveys underestimate
their contamination from highly clustered galaxies at z=1 and stars. We
consider the consequences of this for both the rest-frame ultraviolet
luminosity function and the clustering signal from z=5 galaxies. We also find
that sources with moderate strength Lyman-alpha emission lines can be omitted
from dropout surveys due to their blue colours, again effecting the derived
luminosity functions. We discuss the points of comparison between different
samples, and the applicability of survey-specific results to the population at
z>5 in general.
