My Reading on ASQ CQA HB Part V Part 2

Charlie Chong/ Fion Zhang
Part VE
Judgmental Sampling- Not Statistically Valid
Judgmental sampling can be used by auditors to get a pretty good idea of what is happening, although the
results are not statistically valid. In the first approach, the auditor selects samples based on his or her best
judgment of what is believed to give a representative picture of the population. These samples are chosen
based on the auditor’s past experience. Often these samples are taken from areas that expose the company to
the greatest risk, such as high-dollar orders, special orders, or critical application orders.
The auditor may already know from past history (past audits) that problems have existed in department A,
activity C, and with this knowledge, the auditor examines that area in an audit. In judgmental sampling, the
auditor may also decide to look at all orders over $2 million or all orders destined for installation in the military
aircraft. If a problem is found, the auditor examines additional samples to determine the extent of the
immediate problem. In the second approach (that is, looking at all orders over $2 million), the process or
system has reached maturity, and very few problems are identified in a general audit using random sample
techniques. The company may then decide to audit all areas in which problems were identified, with the
intention of determining whether the activity can be improved beyond its current level.
The nuclear industry and several other industries have reached this point and have begun to rely on
judgmental sampling to identify areas for improvement.
The pro side of judgmental sampling is extensive. The auditor focuses on areas where previous problems were
found and corrected. High-risk areas and activities historically have received the most attention from
management. By doing judgmental sampling, the auditor will be providing information on areas known to be of
interest to management. Judgmental sampling allows companies to focus their efforts on specific
improvements rather than general assessment. It allows the auditor to more effectively use his or her time
during the audit. And finally, selection of the audit sample is relatively simple, which leaves more time to
prepare for and perform the audit.