Screening is not particular good

Assuring health and safety by screening is usually a bad idea.  While there may be occasional benefits for a few individuals, it works poorly for populations, has unexpected negative consequences and is very inefficient.  This blog has previously pointed out that ISO management accreditation is a screening test with weak performance characteristics.  Its performance characteristics are so poor it would be rejected by any respectable lab if it were a diagnostic test for quality.  UKAS would reject its own performance if it measured itself by the standards it uses to measure others.  If the standards applied to drug trials were applied to UKAS, it would be history.

Devon Zagory explains in Food Safety News how poorly screening works to assure food safety.  Click through and read:

Microbial Testing of Fresh Produce: Where is the Value?

At first glance, it’s counter-intuitive.  But probability tables show clearly that the chance of rejecting a lot of food because of finding a pathogen is extremely low unless the number of samples is prohibitively large.

“At these contamination rates, testing 60 samples, the standard sample size in commercial produce testing, is very unlikely to detect a contaminant. So what is the value of these testing programs? Large testing programs can inform us of general rates of contamination in a population of products. Large testing programs may uncover regional differences in contamination rates. Properly constructed, large testing programs can help validate whether specific interventions, such as water purification or compost preparation, are reducing contamination rates. What pathogen testing programs are not particularly good at is detecting and removing contaminated lots of produce from commerce. Testing is expensive and intrusive and unlikely to detect pathogens, even in the exceptional case when they are present. Commercial operations simply cannot test enough samples, or large enough samples, to have a reasonable probability of detecting pathogens.


“Product testing for the presence of human pathogens is an insensitive tool and an inefficient use of food safety resources. Those resources are likely to be more effective in enhancing food safety if they are invested in HACCP-based preventive programs. If testing for pathogens is to be done, it is more effective to perform the testing in the field before the products reach the handling facility.”

It makes much more sense to analyse the hazards and control the critical points that control them.  That is much more efficient.  It happens all the time and is not “just a sampling exercise” like UKAS inspections.

Read the article.  Analogize that significant errors in lab testing are like pathogens in food. The only time UKAS inspections can do much good is when a lab is really, really bad.  Just as screening foodstuffs is only efficient when there is widespread contamination. In which case, the market would find that out soon anyway.  The bad lab would be put out of business by competitors that produce better work.  Even UKAS rarely forgoes its fees to remove accreditation from a lab – the number is publishes every year is very low.

Accreditation bodies know perfectly well that their contribution to real quality is negligible.  That’s why they must distract the fee-payers by keeping them focused on mere “non-compliances” with the inspection cartel’s standards. 

Almost nobody sees that most non-compliances are unimportant to the validity of the tests.

You can’t inspect quality in any more than you can inspect microbial safety into food.  Both must be controlled by knowledgeable, high quality staff, not inspection-passing drones trained to be content to comply rather than to think.



This entry was posted in Bureaucracy, Cartel, Economics, Laboratory medicine, Science and tagged , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s