Stats Chat

From news.com.au (via @LewSOS and @Economissive on Twitter) “The names of Australians most likely to win the lotto have been revealed, with the top three taking home more than a quarter of the prizes last year.”

What they actually have for ‘names’ is first initials. Apparently, more than a quarter of first-division prizes last year were won by people whose names started with “J”, “A”, or “D”.  Of course, people whose names start with these letters are not any more likely to win lotto if they buy tickets. Either more people in this category bought tickets than average (in which case it would be truer to say they are more likely to lose Lotto), or the distribution of initials is pretty much the same as for the country as a whole.

The story does go on to say that name and age can’t affect your chance of winning, but not to explain why, given that, it’s news.

Anyway, since Rob Hyndman and the stats group at Monash have put together a database of frequencies of Australian names, we can see how representative the winners are.  Here are the proportion of Oz babies born each year (up to current 18-year-olds) whose names begin with “J”, “A”, or “D”. As you can see, it’s “more than a quarter” almost every year where we have data.

Since you’re a StatsChat reader, you can probably think of reasons there might be a difference between Lotto name frequencies and baby name frequencies.  The baby names don’t include immigrants and do include emigrants.  There might be ethnic differences in propensity to play Lotto that happen to be correlated with first initial. There might be quite large chance differences because the lottery folks only looked at first-division winners, a very small (but random) sample of Lotto players. But it doesn’t look like we need to go there.

Team Ratings for Round 23

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 150 matches played, 101 of which were correctly predicted, a success rate of 67.3%.
Here are the predictions for last week’s games.

Predictions for Round 23

Here are the predictions for Round 23. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Postponed Games

Another week where there were postponed games that eluded me. I have included these forecasts for completeness.

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 150 matches played, 99 of which were correctly predicted, a success rate of 66%.
Here are the predictions for last week’s games.

Predictions for Postponed Games

Here are the predictions for Postponed Games. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Week 12

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 41 matches played, 28 of which were correctly predicted, a success rate of 68.3%.
Here are the predictions for last week’s games.

Predictions for Week 12

Here are the predictions for Week 12. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Round 9

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 64 matches played, 44 of which were correctly predicted, a success rate of 68.8%.
Here are the predictions for last week’s games.

Predictions for Round 9

Here are the predictions for Round 9. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Congratulations to Dr Sally-Ann Harbison for her award of membership to the NZ Order of Merit in the New Year’s honours list of 2021. This acknowledges her service to forensic science.

Dr Sally-Ann Harbison leads the Forensic Biology Team at the Institute of Environmental Science and Research (ESR). Dr Harbison has a joint appointment with the University of Auckland’s Department of Statistics.

Dr Harbison initially joined ESR’s precursor, DSIR, in 1988 in the chemistry division, where she focused on crime scene and evidence examinations including identifying body fluids and blood grouping.

Her work led her to play a significant part in many prominent New Zealand cases. With ESR, she has been a major contributor to the development and application of New Zealand’s Forensic DNA capability. In 1999 she worked on the first homicide case that was solved by using the DNA Profile Databank.

She has been the case manager in a number of old cases that are being reviewed with more modern DNA methods. She has collaborated with colleagues worldwide and represented ESR on various international committees. She has spoken at many international conferences and meetings and written more than 60 publications in her field. She has taught at University of Auckland since 1996, supervising more than 60 MSc and PhD students.

Dr Harbison has led the Biology Specialist Advisory Group of the Australia/New Zealand Forensic Executive Committee and been an assessor for both Australian and American accreditation bodies.

• Mediawatch took on bogus polls and interviewed me.
• If you ask people whether the recent stories about blood clotting affect their views on Covid vaccines they will say ‘yes’. But if you asked people, before and after, what their views actually are, there’s a very slight change to be more pro-vaccine.
• A study of 9806 blood donors found 8 had antibodies to the Covid virus.  Extrapolated crudely to all of NZ that’s about 4000 undiagnosed cases. I’m not giving a statistical uncertainty interval because the non-sampling uncertainty is going to be larger — blood donors tend to be younger and so more likely to have been asymptomatic/weakly symptomatic and thus not tested, but might also be less likely to have been infected.  Still, the number is in the sort of range you’d expect.

There’s a new research paper out from the Christchurch Health and Development Study, which recruited a group of people when they were born, in mid-1977, and has been following them ever since.  Those of the participants who were parents have been asked about physical discipline of their children on four occasions: when they were 25, 30, 35 and 40.  Obviously, over time, the number who are parents has increased (from about 150 to over 600), and the children have (on average) gotten older — when the parents were 25, most of the kids would have been pre-school; the group now includes a few very young children but many who are teenagers.

The good feature of birth cohorts like the Christchurch study is that you get to see the same people throughout the course of their lives; the bad feature is that at any given time everyone is exactly the same age.  In statistician jargon, age is completely confounded with period: you are completely unable to distinguish effects of ageing from time trends. When you see that the proportion of parents reporting hitting their kids has gone down from 77% to 42% over the 15 years, you can’t tell, at all, whether this is an effect of these specific parents getting older and more experienced or an effect of parents in general being less likely to hit their kids.  It’s hard (though not impossible) even to tell if it’s an effect of the kids being older.

As you’d hope, the research paper, in the NZ Medical Journal (paywalled) is very clear on this

…explanations include: increasing maturity of the parenting sample over time (less reactive, more experienced, older parents); a cultural shift towards the unacceptability of violence towards children over the period of the study; and the law change in 2007, which prohibited physical punishment and violence towards children. Given the nature of its design, it is not possible for the current study to distinguish between these explanations.However, it does not seem unreasonable to conjecture that all three processes are likely to have played a role.

And indeed it doesn’t seem unreasonable, as long as you recognise that the not seeming unreasonable isn’t a conclusion from the data and relies entirely on external plausibility.  The researchers do conclude that there’s still a lot of physical punishment going on, and that efforts are needed to stop it; the former is well-supported by the data and the latter is a policy response, not a scientific conclusion. That’s all good.

So let’s look at the reporting (some of this may have changed before or after I read it, of course)

• Radio NZ: Number of parents smacking children drops by half in 15 years. No caveat about the study design meaning this conclusion is basically unsupported. Gets the journal name wrong.
• 1 News: More than 40% of parents still use physical discipline years after law change, latest data shows. The story is better than the headline, and the Children’s Commissioner is quoted as saying “It’s representative of one cohort born in 1977, one group in one year in one generation, but there has been a discernible drop over the years.” I’d be happier if it was clearer from the beginning that this doesn’t claim to be representative of NZ in general over time.
• NZ Herald. Parents’ physical punishment of children decreasing, but still common – report. Slightly better headline; much clearer in the story. “…the rate of physical punishment against children was higher when parents were younger, and then decreased with age… because of the way the study was designed, it couldn’t pinpoint how much the rates reduced because of the law change.”
• Otago Daily Times. Parents still smacking, study finds. Good. “The authors warned that their method of studying a cohort of people over time meant they could not gauge what the attitude of new parents in 2021 might be to physical punishment. However, the research did suggest rates of smacking or hitting children were high enough to be a public health concern.”
• Stuff. Physical punishment of children still ‘fairly common’, despite anti-smacking law change – study.  There’s no caveat about the study design, and the story says “New research, published in the New Zealand Medical Journal on Friday, examined how the prevalence of child physical punishment changed in the 15-year period between 2002 and 2017 – before and after the legislation came into force.”, which isn’t true. And that’s not a link to the research paper.
• Newshub. Who’s most likely to use physical discipline against their kids revealed. The headline’s a bit dodgy given the non-representative group of parents, but the caveats are good “Because the study followed a cohort of parents who aged 15 years over the course of the study, “it is unclear what rates of physical punishment of children would be in studies of contemporary young parents”.

Team Ratings for Round 23

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 146 matches played, 99 of which were correctly predicted, a success rate of 67.8%.
Here are the predictions for last week’s games.

Predictions for Round 23

Here are the predictions for Round 23. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Week 11

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 38 matches played, 25 of which were correctly predicted, a success rate of 65.8%.
Here are the predictions for last week’s games.

Predictions for Week 11

Here are the predictions for Week 11. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.