THE SANITARIAN’S FILE
By Robert W. Powitz, Ph.D., MPH
Sampling, Part 2:
Sampling Strategies
My entire career is dedicated to con- tamination control, whether it involves food, water, air, institutional housekeep-
ing, laundry or manufactured goods. I
learned that the basic, scientific applica-
tions used in contamination control re-
mained the same with each system—only the vocabulary differs
within each industry. The basic objective of contamination control is
to keep the contaminants out: for those that cannot be kept out,
minimize their entry; for those whose entry cannot be minimized,
keep them from dispersing or multiplying; and for those whose
movement and propagation can’t be prevented, get rid of them.
At each point along this continuum, we have to know the scope of the problem, along with how, where, when and why to introduce any cost-effective controls. All of this begins with observation—as in inspection, auditing,
enumeration—and sampling. This, in turn, brings me to the point of this column’s
topic: selecting appropriate sampling strategies that will ultimately guide a course
of action, whether it is in the area of food production or, as is case with many practitioners in my profession, regulatory control and oversight.
Strategy Selection
My introduction to selecting sampling strategies came while I was working at
Wayne State University. I decided to broaden my knowledge of field sampling by
learning as much as I could about how it was done. The only resources that were
readily available in southeastern Michigan were offered by the automotive and
pharmaceutical industries. These industries regularly sponsored a series of tutorials
on monitoring and process validation,
which I was fortunate enough to attend.
My epiphany came while listening to a
lecture sponsored by The American Sup-
plier Institute Inc. on quality engineer-
ing, specifically, designing quality into
products and processes. The author of
the system being presented in this lec-
ture was Dr. Genichi Taguchi of the
Asian Productivity Organization. The
unique concept he developed to look at
tolerance and experimental design in-
volved a series of orthogonal polynomi-
als, a no-nonsense approach. While this
method of sampling is better suited to
mass production of food products than
to regulatory compliance, it did teach
me about selecting specification toler-
ances, the importance of eliminating
bias and the variables to consider in set-
ting up a sampling scheme. Subse-
quently, this information translated
quite well into my world of food safety
inspections and audits.
Strategy Types
So, after that long, drawn-out introduction, I’ll try to cut to the chase. All
field sampling strategies fall into two,
