The method of systematic sampling can be alternative to
simple random sampling and specially preferred when the
information required to construct a sampling is available in
a list or any other organized form. Although systematic
sampling is used for its convenience of drawing and
execution, but its variance of estimator requires some
assumptions about the underlying population order. Some
of these assumptions are whether the population elements
follow particular order, constant mean within strata, or the
population is assumed to be either linearly increasing or
decreasing in the variable of interest