Posts from February 2015 (33)

Here’s a graph from the Economist showing the impact of the measles vaccine:

The number of measles cases fell from over half a million per year to about 100 per year when the vaccine was introduced. That’s a 99.98% reduction, in a disease that (in a healthy population) kills about two people in a thousand.

Here’s a graph from the Centers for Disease Control showing that little blip in 1990 on an expanded scale:

They say

The most important cause of the measles resurgence of 1989–1991 was low vaccination coverage. Measles vaccine coverage was low in many cities, including some that experienced large outbreaks among preschool-aged children throughout the early to mid-1980s. Surveys in areas experiencing outbreaks among preschool-aged children indicated that as few as 50% of children had been vaccinated against measles by their second birthday, and that black and Hispanic children were less likely to be age-appropriately vaccinated than were white children.

Vaccine coverage isn’t as bad as that now, but the profile of unvaccinated kids is different. Black and Hispanic children are just as likely as white children to have had at least one doses of the measles vaccine, and children in poverty have a rate only 1.5 percentage points lower. Now, a substantial chunk of the problem is parents who are anti-vaccine.

Kieran Healy has an interesting post on the ‘personal belief exemption’ data for kindergarten children in California.  They are only 3.36% of children, but they cluster.  That’s important because US is just on the edge of having high enough vaccine coverage to stop an epidemic from spreading, at least if the unvaccinated were evenly spread through the population. They aren’t:

the number of kindergarteners with PBEs, even in Berkeley, is not huge—about 67 kids out of 850 in the city. But 20 of those 67 are in the same school, and probably the same room.

Anti-vaccine hysteria is more prominent in the US than New Zealand: partly because our mainstream media don’t go in for it, and partly because everything is more prominent in the US. Similarly, reaction to the risks posed by unvaccinated children has been more prominent in the US. However,  New Zealand has a similar rate of measles vaccination. Our schools or early childhood services cannot refuse enrollment based on vaccination (no special paperwork is required as in California), and (like California) can only temporarily exclude unvaccinated children if they are known to have been exposed.

Last year, New Zealand had 283 cases of measles. Scaled for population, last year in NZ was about half as bad as the US in 1990, and about thirty times bigger than the current US outbreak (so far).

Every year, the Department of Statistics offers summer scholarships to a number of students so they can work with staff on real-world projects. Daniel, right, is working on a project called Working with data from conservation monitoring schemes with Associate Professor Rachel Fewster. Daniel explains:

“The university is involved in a project called CatchIT, an online system that aims to help community conservation schemes by proving users with a place where they can input and store their data for reference. The project also produces maps and graphics so that users can assess the effectiveness of their conservation schemes and identify areas where changes can be made.

“My role in the project is to help analyse the data that users put into the project. This involves correctly formatting and cleaning the data so that it is usable. I assist users in the technical aspects relating to their data and help them communicate their data in a meaningful way.

“It’s important to maintain and preserve the wildlife and plant species we have in New Zealand so that future generations have the opportunity to experience them as we have. Our environments are a defining factor of our culture and lifestyles as New Zealanders and we have a large amount of native species in New Zealand. It would be a shame to see them eradicated.

“I am currently studying a BCom/BA conjoint, majoring in Statistics, Economics and Finance. I’m hoping to do Honours in statistics and I am looking at a career in banking.

“Over summer, I hope to enjoy the nice weather, whether out on the boat fishing, at the beach or going for a run.”

Every year, the Department of Statistics offers summer scholarships to a number of students so they can work with staff on real-world projects. Ole, right, is working on a project called Testing data-model fitness in phylogenetics with Dr Steffen Klaere. Ole explains:

“A continuously elusive question in phylogenetic inference is how to test data-to-model fitness. While there have been omnibus tests available for more than 20 years, their applicability was restricted due to issues of power and computability of the test statistics.

“In recent work, we have assessed the fitness of each site (or observation) separately by fitting simultaneous confidence regions.

“However, the more appropriate choice would be to do informed multiple testing on the sites and identify those sites for which the test finds evidence against model fitness. My task is to investigate a number of potential tests and assess their strength and weaknesses through simulation approaches.

“The maximum likelihood approach for phylogenetic inference resembles to some degree a logistic regression approach. Here, one uses deviance measures to assess the model-data fitness. Such approaches have been tested in phylogenetics as well, however, they often ignore the fact that the data are over-dispersed and zero-inflated.

“Consequently, in my project I will investigate the suitability of corrections to the deviance made by ecologists to account for overdispersion and zero-inflation to build statistics which are suitable to test model-data-fitness in phylogenetics.

“I am studying a masters in mathematics at the Ernst-Moritz-Arndt University Greifswald in Germany. I have a bachelor’s degree in biomathematics, also from Greifswaldl.

“Statistics is one of my favourite topics in mathematics. Statistics plays a big role in finance, economy and nature, and that’s why I want to learn and understand statistics.

“Over summer, I am looking forward to travelling around New Zealand. I want to learn more about this exciting country – it is completely new to me.”