There are a number of ways to address the problems associated with obtaining
an unrepresentative sample from a population. One method for dealing with this issue
is to involve a more structured sampling scheme than simple random sampling. Such
approaches include stratified sampling schemes, proportional sampling, and the use of
concomitant variables to help in selecting appropriate sampling units for measurement.
All of these approaches provide more structured sample data than that resulting from a
simple random sample scheme. Note that this additional structure about which items
to collect and measure is imposed on our data collection process prior to the actual
decision, and, as such, is correctly viewed as a sampling technique.