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
In the Herald this week
New Zealanders are spending more time online than ever, with 50% of respondents spending four or more hours of their leisure time on the internet each day, according to a study commissioned by InternetNZ.
But that doesn’t necessarily mean doom-scrolling TikTok.
The result is partly because of the changing way that more traditional media is delivered.
Watching a couple of hours of TVNZ+ on the smart TV in your lounge or listening to Spotify during your commute counts towards your total.
That’s a nice start — giving the headline result and then contextualising it. I was hoping then to see whether streaming more traditional media did in fact account for the increase. No more mention.
If we look at the report itself, there’s a good description of the survey: a sample of 1001 people, sampled and weighted to be representative of the subset of the NZ population who are online. What does the report say about the increase?
Half of New Zealanders* (50%) spend four or more hours a day on the internet for personal
use.
This is a slight, but not statistically significant, rise from 2023 findings.
In 2023 the number was 46%, and a four percentage point change is relatively unimpressive compared to the sampling uncertainty. The report doesn’t estimate how long we spend doing each activity on the internet, but the proportion of people who use the internet for streaming is about the same this year as last year or maybe slightly higher (42% vs 39%)
The report is generally interesting and useful, with the usual caveat that it’s self-reported — people may not be entirely accurate when you ask them how much time they spend online or how much they know about AI or whatever.
The Washington Post writes about cervical cancer: the vaccine works. This isn’t new news: we know the vaccine stops infection with cancer-causing strains of the human papillomavirus (that’s why it was approved). We know the vaccine stops cervical cancer: the first reliable data came out a few years ago. Now the first cohort of vaccinated girls is old enough that we’re seeing the reduction in cervical cancer deaths.
Using data from the National Center for Health Statistics, researchers looked at cervical cancer deaths in three-year blocks of time. Between 1992 and 2021, there were 398 cervical cancer deaths reported among women younger than 25. During the period of 1992-1994 to 2013-2015, mortality from cervical cancer gradually declined 3.7 percent each year. The period of 2013-2015 to 2019-2021 saw an even greater drop to 15.2 percent annually, according to the study.
The number of deaths decreased from 55 in 1992-1994 to 35 in 2013-2015 to 13 in 2019-2021.
“Assuming that the trend from 1992-1994 to 2013-2015 would have continued, an estimated 26 additional cervical cancer deaths would have been expected to occur between 2016 to 2021, based on projected mortality rates,” the authors wrote.
That description seems like a hard way to present this graph from the article in JAMA (perhaps copyright is the problem?)
The squares are what happened in reality. The orange line shows the downward trend we were seeing before the vaccine, due to better testing and treatment. As you can see, the last two squares, post-vaccine, are dramatically below the orange line. Below is good.
Earlier this week, Wikipedia’s front-page “Did you know…” section this week referenced the year that Vatican City had the world’s highest murder rate. In 1998, a double homicide in the Swiss Guards put the murder rate over 200 per 100,000 inhabitants, more than twice the rate in any of the Caribbean countries that usually head the list and roughly infinity times the usual rate in recent years when it has been a separate country. That’s a real rate, with the right denominator, it’s just that the year to year variability makes rates a relatively unhelpful summary.
Vatican City has a denominator problem for minor crimes; in 1992 there were 392 ‘civil offences’ and 608 ‘penal offences’, working out to a bit less than 100% and a bit more than 100% of the number in resident population. The problem is that the tiny state has many millions of visitors per year and they, rather than the resident population, are both the perpetrators and victims of the minor crimes. The resident population isn’t the right denominator.
A less dramatic version of this problem showed up when looking at rates of violent crime in parts of central Wellington some years back.
The New York Post is saying
Attention-deficit/hyperactivity disorder is a common behavioral condition that affects approximately 7 million US children, including about a million kids diagnosed since 2016.
The reason for the recent rise in diagnoses is under debate — a new study in the journal Nature Mental Health suggests the culprit could be in your medicine cabinet.
They’re talking about paracetamol (or as Americans call it, acetaminophen). There’s a new study that looks at a fairly small group of US mothers and kids and finds weak evidence of a correlation between ADHD diagnosis in the kid and use of paracetamol by the mother. You might remember this topic from previous StatsChat episodes. There was originally a Danish study that was surprised to stumble across a correlation. A New Zealand study checking up on the correlation also found it.
A Spanish study resulted in the NZ Herald (from the Daily Mail) scare headline One paracetamol in pregnancy could raise risk of autism. This was especially egregious since not only did the study say nothing about ‘one paracetamol’ and wasn’t really about autism, it actually found lower rates of the symptoms in kids whose mothers took paracetamol. The study argued that while the rates were lower in those kids, they should have been even lower based on other risk factors. At this point it was all plausible and maybe a bit concerning but not reason for major change in medical practice — after all, mothers aren’t taking Panadol for fun.
In 2023, a combination of most of the published studies estimated a slight increase in risk, about 25%. On the other hand, A very big Swedish study, using data from everyone born in Sweden from 1995 to 2019, then found no suggestion of a correlation.
So what’s the point of this new study? Well, one of the issues in interpreting these correlation studies is that many of them didn’t know for sure who actually took paracetamol. For normal people this would be a big issue — lots of medications include paracetamol, and you might easily miss some, or just forget. Pregnant women, though, tend not to just casually take cough syrup or whatever. Even so, if you happened to have data lying around from blood samples which told you who had taken paracetamol, you might be interested in seeing what the correlation was like. So they did. And the correlation was broadly similar to what the small, early studies had seen: kids whose mothers blood samples showed paracetamol were about twice as likely to have ADHD. That’s nice to know, even if it’s not a big change in the evidence.
We still have the conflict between ‘no sign of a correlation’ in the big Swedish study and ‘about 25% higher’ in the combined smaller studies. It’s possible that paracetamol has an effect and that the Swedish study missed it because it didn’t measure paracetamol use as accurately. It’s also possible that the reasons for taking paracetamol (eg illness, fever) are what causes ADHD. Or it could all be some sort of bias and the Swedish study could be correct. It’s hard to tell. Ask your doctor, etc.
The new study, of course, does not suggest paracetamol is responsible for recent trends in ADHD diagnosis: that claim is down to the New York Post, and is pretty clearly wrong. Here’s the trend:
Paracetamol became popular as a relatively safe, over-the-counter treatment a long time ago now. It might have been response for an ADHD trend in, say, the 1980s, but not a trend in the 21st century.
Q: Did you see that ibuprofen prevents dementia?
A: No
Q: Common 3p anti-inflammatory pill ‘can help prevent dementia’ says new study. And Prolonged Use Of Anti-Inflammatory Pills May Help Prevent Dementia: Study. And…
A: No
Q: Those quotes in the first headline imply someone really said it
A: Well, that used to be the convention, but apparently not in this case.
Q: Mice?
A: No, not mice. People
Q: Correlations, or randomised trials?
A: Correlations
Q: Is there a paper?
A: There is a paper.
Q: Has anyone looked at this correlation before?
A: Oh my yes. So many people. There are even randomised trials. The Cochrane Review says “no evidence that it works, and it may be dangerous”
Q: What do the scientists say about that?
A: The trials were too short to show the effect, or they started too late in the disease process.
Q: Is that possible?
A: Sure, it’s possible. Lots of things are possible.
Q: So you don’t believe the paper?
A: It’s a perfectly reasonable paper for consenting scientists in private (I know some of the authors), but it doesn’t justify the recommendation of long-term treatment with these drugs for the prevention of dementia, especially given the potential adverse effects
Q: Well, that’s your opinion. What do the scientists who wrote the paper say?
A: Our results.. do not justify the recommendation of long-term treatment with NSAIDs for the prevention of dementia, given its potential adverse effects.
“Bowel cancer does not discriminate on race. Māori and Pacific peoples have a similar risk of developing bowel cancer compared to other population groups at a given age.“It was true that a higher proportion of bowel cancers occur in Māori and Pacific peoples at a younger age, but that is because the overall demographics of those groups are younger. It has always been age that determines bowel cancer risk, not race”I thought that this required more explanation. Proportion at an age does not seem to me to depend on the demographics of those ages
It’s a good question. The minister is plausibly correct that the younger age at diagnosis for Māori and Pacific Peoples is driven substantially by demographics. That is, one reason that few very elderly Māori get diagnosed with bowel cancer is that there aren’t many very elderly Māori. Fewer Māori make it to be very elderly, and also the Māori population is increasing both because of higher birth rate and because more people are now identifying as Māori to the healthcare system. If you have the same age-specific incidence rates in two groups, but one group averages younger, the incidence in the younger group will tend to be at younger ages.
That’s not the whole story, or even most of it, for this decision. The age distribution being quoted is age at diagnosis (because that’s what you have for cancer), but diagnosis isn’t equally distributed. According to the HQSC atlas of health care variation, Māori are more likely to be diagnosed with bowel cancer following emergency presentation, and more likely to die within two years of diagnosis. This means there’s a good case that Māori are more underdiagnosed than New Zealand Europeans. On the other hand, a lot of the problem with underdiagnosis is not being tested. If people end up just doing one test when they become eligible, and then not bothering later, the optimal age for a single test is more like 60 than 50. And, as a general principle, if you want to spend public money to improve health, you typically will do better by spending it on people who are less healthy and have worse access to health care.
In any case, while the headline Bowel cancer screening eligibility age to be lowered for everyone is technically true (since the lower-age screening pilot has already been stopped), it seems to miss the point a little.
NZ$ Herald has a piece today about increases in methamphetamine consumption (as measured by wastewater)
The story is about cheap meth imports increasing the supply, with a speculative aside into a decrease in consumption in Ōpōtiki and whether it might be attributable to major gang arrests.
The sudden spike in 2024 is surprising. Normally I would guess that sudden level changes in a time series were due to different definitions of the variable, but it appears to be defined the same way.
It’s obviously tempting to attribute the sudden change to the relaxation of rules on pseudoephedrine sale in 2024, and some people on social media seemed happy to do so. There are problems, though.
First, the suddenness is still strange. You’d expect the gangs to take a while to ramp up production and sale after years out of the business — and if they were ready on day one, the spike would have been in June rather than July.
Second, that’s a big spike. There’s about gram and a half of pseudoephedrine in a pack of decongestant tablets, which will make under a gram of meth, so a 20kg jump in meth production is a lot of Sudafed: tens of thousands of packets per week of a drug sold only by pharmacist prescription. Someone should have noticed.
The Drug Foundation says it’s due to international supply, which seems plausible — we’re seeing 300-500kg seized most quarters recently, which is 15-40kg/week, so unless we’re catching the majority there will be enough getting through to explain wastewater levels.
The Herald also quotes price data from the Drug Trends Survey, which says prices are down. That’s a bit less supportive than it looks. First, prices were only down in roughly a straight line over several years. Second, the say they think demand has saturated, which doesn’t fit the spike. And finally, the last edition of the survey sampled from February to July 2024, so mostly missed the spike
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