Are beneficiaries increasingly failing drug test?
Stuff’s headline is “Beneficiaries increasingly failing drug tests, numbers show”.
The numbers are rates per week of people failing or refusing drug tests. The number was 1.8/week for the first 12 weeks of the policy and 2.6/week for the whole year 2014, and, yes, 2.6 is bigger than 1.8. However, we don’t know how many tests were performed or demanded, so we don’t know how much of this might be an increase in testing.
In addition, if we don’t worry about the rate of testing and take the numbers at face value, the difference is well within what you’d expect from random variation, so while the numbers are higher it would be unwise to draw any policy conclusions from the difference.
On the other hand, the absolute numbers of failures are very low when compared to the estimates in the Treasury’s Regulatory Impact Statement.
MSD and MoH have estimated that once this policy is fully implemented, it may result in:
• 2,900 – 5,800 beneficiaries being sanctioned for a first failure over a 12 month period
• 1,000 – 1,900 beneficiaries being sanctioned for a second failure over a 12 month period
• 500 – 1,100 beneficiaries being sanctioned for a third failure over a 12 month period.
The numbers quoted by Stuff are 60 sanctions in total over eighteen months, and 134 test failures over twelve months. The Minister is quoted as saying the low numbers show the program is working, but as she could have said the same thing about numbers that looked like the predictions, or numbers that were higher than the predictions, it’s also possible that being off by an order of magnitude or two is a sign of a problem.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
We also don’t know the mix of people tested. If the ratio of males to females changes (i.e. solo mums tested first) than the rate would change as females are less likely to use marijuana – the most popular illegal drug.
9 years ago
Indeed, there’s almost no limit to the things we don’t know.
9 years ago
You can dig into this more here: https://www.fyi.org.nz/request/498/response/3064/attach/html/4/img%20917180843%200001.pdf.html
9 years ago
At least two factors going on – people switching to untestable (or at prohibitive cost) drugs, and decrease in drug testing as businesses tightened belts. I think I heard or saw stats on this at one point but can’t be sure.
9 years ago
To the extent that it’s switching, that means the law change has moved people to more dangerous drugs, and ones that their employers can’t detect reliably.
The synthetic cannabimimetics do seem to make screening for cannabis use counterproductive in terms of public health and safety.
9 years ago