148
Sampling Essentials
• If the selection process is manual, systematic sampling is easier, simpler,
less time-consuming, and more economical than simple random sam-
pling. One needs to use a random process to select only the first element.
On the other hand, if the selection process is computerized, the ease in the
selection process of systematic sampling and simple random sampling
may be comparable to each other.
• If the sampling frame has a monotonic ordering that is related to a study
variable (e.g., ordering of stores by dollar value, listing of employees by
number of years employed, and listings of schools by graduation rates),
implicit stratification may result in the statistical efficiency equivalent to
that of proportionate stratified sampling and is thereby more efficient
than simple random sampling. If the ordering is randomized, systematic
sampling may yield results similar to simple random sampling.
• Systematic sampling ensures that the sample is more spread across the
population.
Table 5.8 Strengths and Weaknesses of Systematic Sampling Compared to Simple
Random Sampling
Strengths Weaknesses
Unlike simple random sampling: Unlike simple random sampling:
If the selection process is manual, systematic
sampling is easier, simpler, less time-consuming,
and more economical.
If the sampling interval is related to periodic
ordering of the elements in the sampling
frame, increased variability may result.
The target population need not be numbered
and a sampling frame compiled if there is
physical representation.
Combinations of elements have different
probabilities of being selected.
If the ordering of the elements in the sampling
frame is randomized, systematic sampling may
yield results similar to simple random sampling.
Technically, only the selection of the first
element is a probability selection since for
subsequent selections, there will be elements
of the target population that will have a zero
chance of being selected.
If the ordering of the elements in the sampling
frame is related to a study variable creating
implicit stratification, systematic sampling is
more efficient than simple random sampling.
Principle of independence is violated, for the
selection of the first element determines the
selection of all others.
Systematic sampling eliminates the possibility
of autocorrelation.
Estimating variances is more complex than
that for simple random sampling.
Systematic sampling ensures that the sample is
spread across the population.