Many times in statistical applications, there seems to be some question as to whether

Many times in statistical applications, there seems to be some
question as to whether or not the data properly represent the population
from which a sample is drawn. In this case, two different levels of
statistics come into play—parametric 
and non-parametric statistical
applications.

Discuss in detail the differences of each type and appropriate use in
data analysis using citations and references to 
validate your argument.