Quarter of a million meth labs? (updated)

3 News says “Tests find meth traces in 40pc of houses“.

Now, this is only rentals, but according to the Census there are 563000 rental dwellings in the country, so 40% would be nearly quarter of a million.  If you’re marketing the test as detecting meth labs, this statistic implies either a hugely unrepresentative sample or a test with a high false-positive rate.

In fact it’s probably potentially both. The sample is dwellings where the landlord bought a test from the company MethSolutions, so you’d hope they were higher-risk than average. and the

[MethSolutions] director Miles Stratford told 3 News the results varied from low-level meth use to high-end meth manufacturing.

So the test is picking up both traces of use and unrelated activity in additional to actual manufacture of methamphetamine. Mr Stratford believes [via email to me] that low-level traces of use are still a health risk. I am unconvinced and would count them as false positives, but it’s  not invalid for him to count them as true positives.

[This next quote was about the surveillance product MethMinder, not about the tests: I shouldn’t have conflated them]

“Some of the instances that we’ve found are people using industrial cleaner inside of properties. We’ve had instances where there have been low-grade plastics fires that have produced a whole bunch of volatile gases into the air that have been picked up.”

The company website doesn’t give any information, as far as I can tell, about either the false positive or false negative rate of the tests — they mention Ministry of Health guidelines, but these guidelines are for remediation of known meth labs, not for screening. [Mr Stratford’s subsequent email says that his lab tests have essentially no analytic false positives — ie, if they say there is meth, there is at least some meth present]

And if you’re thinking about using this service you should, of course, read their terms and conditions, which disclaim any guarantees of any level of accuracy, disclose that the service is subsidised by referrals of positive tests to clean-up companies

Where an indicative test is undertaken on behalf of or for the benefit of the owner of a property and that owner or their insurer chooses not to utilise MethSolutions dedicated service providers in quantifying and/or decontaminating and/or reinstating a property, an additional charge of $200 + GST will be due and payable for each of these services that is not utilised but which is required in order to ensure a property is fit to be lived in.

and have other interesting section headlines such as “MethSolutions Is not an Environmental Testing or Security Company” and “No Guarantees on Cost of Sampling.”