The Physics Police

The Physics Police

Saturday, September 27, 2014

Measles Vaccine Efficacy in China

For whatever sick reasons, anti-vaccine activists try to use fear to dissuade parents from vaccinating their children. Make no mistake. This is an act of pure evil. Not only does it leave unvaccinated children at a higher risk of catching serious, sometimes fatal contagious diseases, but it puts everyone around them at increased risk of catching these diseases too. This is what drives many people to fight against the misinformation, myself included.

The name of the game is science denial for the anti-vaccine activist. They have their work cut out for them. Concocting a worldview where a health measure that prevents between 2 and 3 million deaths every year is a bad thing takes a lot of work.

Thankfully, sometimes all we need to do is give them enough metaphorical rope to hang themselves.

Here's an example!

Earlier this year, a study was published to the Bulletin of the World Health Organization on the progress towards the elimination of measles in China.

Sayer Ji, infamous for misrepresentation of scientific articles, in a blog post about the study, says:
China has one of the most vaccination compliant populations in the world. In fact, measles vaccine is mandatory. So why have they had over 700 measles outbreaks from 2009 and 2012 alone? The obvious answer is the the measles vaccines are simply NOT effective.
While the study's conclusion states unequivocally that:
In 2013, most of the resurgence seen in measles cases was the result of the susceptibility of unvaccinated or incompletely vaccinated children...
Which directly contradicts the central claim of Ji's blog post. This is typical of Ji. He consistently references scientific studies in an attempt to lend credibility to his argument despite the fact that the contents utterly refute his argument. He relies on the laziness and lack of education among his readers. If any of them simply read the study, they'd notice that it says the opposite of what he claims.

His biggest mistake was using the word "effective" which, in the study of vaccines, has a rigorous mathematical meaning. The efficacy of a vaccine is defined as:

E = 1 - (V / U)

Where U and V are the "attack rates" in the unvaccinated and vaccinated population, respectively. We calculate these attack rates by dividing the number of sick people divided by the population size. So the first question is, who got sick? The cited study shows 53% of measles sufferers were unvaccinated, while 47% were fully vaccinated.

The anti-vaccine activist might say, "but those percentages are almost the same! It looks like the vaccine hardly made a difference. You've got almost a 50% chance of getting sick either way, right?"

Wrong. And we just need one more piece of information to prove it.

According to the title of Ji's own blog post, "99% are vaccinated." Now we can calculate attack rates:

V = 0.47 / 0.99 = 0.475
U = 0.53 / 0.01 = 53

Which means the efficacy of the measles vaccine in China is:

E = 1 - (0.475 / 53) = 0.991

Or, 99.1% effective, consistent with efficacy noted on the CDC website.

So why is the anti-vaccine activist wrong to suppose you've got a 50% chance of getting sick either way? I like to think of it from the point of view of the measles virus. If I spread randomly from person to person, it will be hard for me to find that one unvaccinated person in a crowd of 100 people. If I do manage to find that person more than 1% of the time, I've done better than chance. That means it was easier for me to infect this person than the other 99 vaccinated people.

It only takes grade school math to expose the likes of Sayer Ji.

Friday, September 12, 2014

Solar Power and Birds

The Ivanpah Solar Power Facility is a "thermal tower" solar plat in the Mojave Desert, California. Rather than converting sunlight directly into electricity as do photovoltaic solar panels, thousands of mirrors reflect sunlight at a central tower. Water in the tower is heated to 1,000 degrees Fahrenheit. The resulting steam runs an electric turbine. Storing solar energy in the form of heat allows the plant to generate electricity 24 hours a day. Latent heat used overnight is replenishing the next day.

This feature allows the plant to avoid the major drawback of other renewable energy production systems, like wind farms and photovoltaic arrays, which only output energy when the wind is blowing, and the Sun is shining, respectively.

Ivanpah Solar Power Facility (No, it's not Burning Man.)
Criticisms of this pilot plant include the cost, and environmental impact. As for the cost, pilot plants are always expensive. Huge savings are typically seen when a technology is scaled up. The facility cost about $5,561 per kW, only one and a half times the cost of building a new coal facility which runs about $3,500 per kW. Anyway, cost is a concern for the economists. I'm interested in the environmental impact, because I'm an environmentalist.

Unforeseen in the Environmental Impact Statement and prior to construction, some birds were found to have been burnt by when they flew into the area of focused sunlight. US Fish and Wildlife Service (FWS) began an investigation in July, 2012.

Shortly after the plant formally opened in February, 2014 the Wall Street Journal ran an attack piece by Cassandra Sweet with accompanying correspondent interview.
A giant solar-power project officially opening this week in the California desert is the first of its kind, and may be among the last, in part because of growing evidence that the technology it uses is killing birds.
This WSJ article leaves out the fact that all buildings with windows kill some birds, and that all methods of generating power harm the environment. The question is, how many birds are killed by this facility due to heat damage from fling into the focal range? And, how does the environmental impact of this facility compare to other types of facilities?

By the time the FWS published a preliminary report of their investigation in April, 2014, the news story was long forgotten. The report got little attention until August, when Ellen Knickmeyer and John Locher published an egregiously misleading article in the Associated Press.
Federal wildlife investigators who visited the BrightSource Energy plant last year and watched as birds burned and fell, reporting an average of one "streamer" every two minutes, are urging California officials to halt the operator's application to build a still-bigger version.
Here's what report actually says about the "streamers":
... these events represent the combustion of loose debris, or insects.
In reality, the report investigation found only 47 birds injured by solar flux in the 1-year study period. So, at least 47 of the "streamers" might have, in fact, been birds. But not all of them. The article attempts to fool its readers by knowingly conflating the streamers with bird deaths. I trust my readers know better than to fall for such an obvious syllogistic fallacy.

Credulous readers of the AP article would walk away thinking that the report showed 5,591 times more bird fatalities than were actually reported. That's misleading by 3.7 orders of magnitude!

How does this compare to some other anthropogenic sources of avian mortality?
  • An estimated 1.4-3.7 billion birds are killed each year by cats.
  • As many as 980 million birds crash into buildings annually.
  • 174 million birds die from power lines every year.
  • Up to 340 million birds perish from vehicles/roads.
  • Approximately 6.8 million birds die flying into communications towers.

And how does this compare to other types of power generation?

Avian Mortality from different types of power generation.

One study compares estimates of the number of avian fatalities per GWh by energy sector.
  • 0.27 for Wind
  • 0.60 for Nuclear
  • 9.40 for Fossil Fuel
Whereas I calculate the total (solar flux + other causes) fatalities per Gigawatt-hour:
  • (141 birds per year) / (1000 Gigawatt-hours per year) = 0.141 for Ivanpah

That's right. The Ivanpah plant costs the least number of bird's lives per Gigawatt-hour. It's terrible to measure electric power in terms of dead birds. But if you really care about protecting birds, you must question whether the benefits outweigh the risks, not to your own political ideology or world-view, but to the birds.

Moral and environmental consideration of a technology must include the cost of the alternatives!

Solar thermal towers help protect birds by replacing more hazardous means to generate power.