Posts from October 2021 (21)

Today is the NZ Vaxathon! I had my second dose last week. All the statisticians I’ve talked to on the issue have had either one or two doses depending on when they became eligible.  For fans of anecdata, our experience varied from no adverse effects at all to a day or so feeling pretty bloody average, consistent with what the randomised trial reported.

In the spirit of StatsChat, here are some links to primary sources for anyone who wants to do their own reading rather than getting clinicians and scientists to translate it

• Official guidance from the US Food and Drug Administration on what sort of evidence they would need to approve a Covid vaccine (June 2020)
• The protocol (plan) for the Pfizer vaccine trial. It’s unusual for these to be public, but it was reassuring when this one was published last year (PDF)
• The meeting briefings for the external expert advisory committee meeting that recommended authorisation of the vaccine. You want ‘Briefing Document -FDA’ and ‘Briefing Document -Sponsor’. And if you’re really dedicated, the transcript of the discussion.  This is where you get all the detailed information that doesn’t fit into a published research paper, plus discussion from the medical and scientific experts
• Real-world effectiveness assessment of the vaccine in Israel. Authors include Miguel Hernán, who is a leading expert on causal inference from observational data
• What we know about heart inflammation after vaccination: an adverse reaction in about one person per 100,000 aged under 40.  Most recover fully, but there has been one death in New Zealand that was probably due to this.
• A summary on vaccine effectiveness with links to primary sources, covering effectiveness against Delta, prevention of infection, and prevention of symptomatic disease
• Vaccination of health care workers in the UK reduced infection rates for their household members
• A recent study in China (with different vaccines) found vaccinated people were less likely to pass on the virus even with Delta
• An even more recent UK study looking at the Pfizer and AZ vaccines found the same

Team Ratings for Week 4

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 24 matches played, 19 of which were correctly predicted, a success rate of 79.2%.
Here are the predictions for last week’s games.

Predictions for Week 4

Here are the predictions for Week 4. 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 7

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 42 matches played, 33 of which were correctly predicted, a success rate of 78.6%.
Here are the predictions for last week’s games.

Predictions for Round 7

Here are the predictions for Round 7. 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 5

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 24 matches played, 12 of which were correctly predicted, a success rate of 50%.
Here are the predictions for last week’s games.

Predictions for Round 5

Here are the predictions for Round 5. 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 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 31 matches played, 18 of which were correctly predicted, a success rate of 58.1%.
Here are the predictions for last week’s games.

Predictions for Round 11

Here are the predictions for Round 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.

A few assorted issues:

First, the denominator questions — not the question of the actual population of NZ, which Henry Cooke is in charge of, but the eligibility and ethnicity questions.

Should we be quoting vaccination as a percentage of those eligible or as a percentage of the population? Yes, both. They answer two different important questions.  There’s a question of epidemic dynamics: are we getting to a point where enough people are vaccinated for Delta to be controllable more easily? What’s relevant there is vaccination as a percentage of the population; kids still count as unvaccinated, even though they aren’t eligible. There’s also a social question: are we providing the right access, information, and incentives to get people vaccinated? What’s relevant there is vaccination as a percentage of those eligible.

Next, ethnicity. I’ve seen people asking how ethnicity is counted in the MoH reports. Most of the NZ government tries to count people according to all the ethnicities they identify with — you can be in multiple categories. As a result, the categories add up to more than 100% of the population. The Ministry of Health does something different. If you give them multiple ethnicities, they pick one.  They prioritise: you’re Māori if that’s one of your ethnicities; you’re Pacific if that’s one of your ethnicities and Māori isn’t; you’re Asian if that’s one of your ethnicities and Māori and Pacific both aren’t, and so on. The advantage of this is that subgroups add up nicely: the number of vaccinations overall is the sum  of the numbers in each ethnic group. The disadvantage is that you may not be in the group or groups you expect.

Finally, pictures like this (this one is from @farmgeek on Twitter)

This is aiming to show the protective effect of vaccines. It’s a lot better than just reporting the % vaccinated among cases or hospitalised cases, because it shows the denominator.  The ratio of the red:green ratios in two bars is an estimate of one aspect of vaccine effectiveness; you can see it’s big.

It’s not a perfect estimate, for two reasons. The first is differences in exposure. If people who are unvaccinated are also more likely to be exposed, the vaccine will look more effective than it is; if people who are unvaccinated are less likely to be exposed the vaccine will look less effective than it is.  Both of these are likely: vaccination and exposure is broadly higher in Auckland than in the rest of the country, but within Auckland vaccination is  higher in areas where exposure is probably lower.

On top of any differences in exposure, a graph like this underestimates the impact of the vaccine because it misses out the reduction in unvaccinated cases due to the vaccine. Getting vaccinated protects you, but as the vaccination rates slowly rise, getting vaccinated also increasingly protects other people, regardless of their vaccination status.  Measles is a good example here: vaccinated people are almost never hospitalised for measles, because the vaccine protects us, but very few unvaccinated people are hospitalised for measles because community vaccination levels slow the outbreaks down enough for testing and tracing to control them.

Team Ratings for Week 3

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 16 matches played, 15 of which were correctly predicted, a success rate of 93.8%.
Here are the predictions for last week’s games.

Predictions for Week 3

Here are the predictions for Week 3. 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 6

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 35 matches played, 26 of which were correctly predicted, a success rate of 74.3%.
Here are the predictions for last week’s games.

Predictions for Round 6

Here are the predictions for Round 6. 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 4

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 18 matches played, 8 of which were correctly predicted, a success rate of 44.4%.
Here are the predictions for last week’s games.

Predictions for Round 4

Here are the predictions for Round 4. 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 10

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 27 matches played, 16 of which were correctly predicted, a success rate of 59.3%.
Here are the predictions for last week’s games.

Predictions for Round 10

Here are the predictions for Round 10. 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.