Archive for the 'Bad Statistics' category

Back to an old topic: Bad Vaccine Math

Jan 25 2013 Published by under Bad Math, Bad Probability, Bad Statistics

The very first Good Math/Bad Math post ever was about an idiotic bit of antivaccine rubbish. I haven't dealt with antivaccine stuff much since then, because the bulk of the antivaccine idiocy has nothing to do with math. But the other day, a reader sent me a really interesting link from what my friend Orac calls a "wretched hive of scum and quackery", naturalnews.com, in which they try to argue that the whooping cough vaccine is an epic failure:

(NaturalNews) The utter failure of the whooping cough (pertussis) vaccine to provide any real protection against disease is once again on display for the world to see, as yet another major outbreak of the condition has spread primarily throughout the vaccinated community. As it turns out, 90 percent of those affected by an ongoing whooping cough epidemic that was officially declared in the state of Vermont on December 13, 2012, were vaccinated against the condition -- and some of these were vaccinated two or more times in accordance with official government recommendations.

As reported by the Burlington Free Press, at least 522 cases of whooping cough were confirmed by Vermont authorities last month, which was about 10 times the normal amount from previous years. Since that time, nearly 100 more cases have been confirmed, bringing the official total as of January 15, 2013, to 612 cases. The majority of those affected, according to Vermont state epidemiologist Patsy Kelso, are in the 10-14-year-old age group, and 90 percent of those confirmed have already been vaccinated one or more times for pertussis.

Even so, Kelso and others are still urging both adults and children to get a free pertussis shot at one of the free clinics set up throughout the state, insisting that both the vaccine and the Tdap booster for adults "are 80 to 90 percent effective." Clearly this is not the case, as evidenced by the fact that those most affected in the outbreak have already been vaccinated, but officials are apparently hoping that the public is too naive or disengaged to notice this glaring disparity between what is being said and what is actually occurring.

It continues in that vein. The gist of the argument is:

  1. We say everyone needs to be vaccinated, which will protect them from getting the whooping cough.
  2. The whooping cough vaccine is, allagedly, 80 to 90% effective.
  3. 90% of the people who caught whooping cough were properly vaccinated.
  4. Therefore the vaccine can't possibly work.

What they want you to do is look at that 80 to 90 percent effective rate, and see that only 10-20% of vaccinated people should be succeptible to the whooping cough, and compare that 10-20% to the 90% of actual infected people that were vaccinated. 20% (the upper bound of the succeptible portion of vaccinated people according to the quoted statistic) is clearly much smaller than 90% - therefore it's obvious that the vaccine doesn't work.

Of course, this is rubbish. It's a classic apple to orange-grove comparison. You're comparing percentages, when those percentages are measuring different groups - groups with wildly difference sizes.

Take a pool of 1000 people, and suppose that 95% are properly vaccinated (the current DTAP vaccination rate in the US is around 95%). That gives you 950 vaccinated people and 50 unvaccinated people who are unvaccinated.

In the vaccinated pool, let's assume that the vaccine was fully effective on 90% of them (that's the highest estimate of effectiveness, which will result in the lowest number of succeptible vaccinated - aka the best possible scenario for the anti-vaxers). That gives us 95 vaccinated people who are succeptible to the whooping cough.

There's the root of the problem. Using numbers that are ridiculously friendly to the anti-vaxers, we've still got a population of twice as many succeptible vaccinated people as unvaccinated. so we'd expect, right out of the box, that better than 2/3rds of the cases of whooping cough would be among the vaccinated people.

In reality, the numbers are much worse for the antivax case. The percentage of people who were ever vaccinated is around 95%, because you need the vaccination to go to school. But that's just the childhood dose. DTAP is a vaccination that needs to be periodically boosted or the immunity wanes. And the percentage of people who've had boosters is extremely low. Among adolescents, according to the CDC, only a bit more than half have had DTAP boosters; among adults, less that 10% have had a booster within the last 5 years.

What's your succeptibility if you've gone more than 5 years without vaccination? Somewhere 40% of people who didn't have boosters in the last five years are succeptible.

So let's just play with those numbers a bit. Assume, for simplicity, than 50% of the people are adults, and 50% children, and assume that all of the children are fully up-to-date on the vaccine. Then you've got 10% of the children (10% of 475), 10% of the adults that are up-to-date (10% of 10% of 475), and 40% of the adults that aren't up-to-date (40% of 90% of 475) is the succeptible population. That works out to 266 succeptible people among the vaccinated, which is 85%: so you'd expect 85% of the actual cases of whooping cough to be among people who'd been vaccinated. Suddenly, the antivaxers case doesn't look so good, does it?

Consider, for a moment, what you'd expect among a non-vaccinated population. Pertussis is highly contagious. If someone in your household has pertussis, and you're succeptible, you've got a better than 90% chance of catching it. It's that contagious. Routine exposure - not sharing a household, but going to work, to the store, etc., with people who are infected still gives you about a 50% chance of infection if you're succeptible.

In the state of Vermont, where NaturalNews is claiming that the evidence shows that the vaccine doesn't work, how many cases of Pertussis have they seen? Around 600, out of a state population of 600,000 - an infection rate of one tenth of one percent. 0.1 percent, from a virulently contagious disease.

That's the highest level of Pertussis that we've seen in the US in a long time. But at the same time, it's really a very low number for something so contagious. To compare for a moment: there's been a huge outbreak of Norovirus in the UK this year. Overall, more than one million people have caught it so far this winter, out of a total population of 62 million, for a rate of about 1.6% or sixteen times the rate of infection of pertussis.

Why is the rate of infection with this virulently contagious disease so different from the rate of infection with that other virulently contagious disease? Vaccines are a big part of it.

10 responses so far

Willfull Ignorance about Statistics in Government

May 21 2012 Published by under Bad Math, Bad Statistics, Politics

Quick but important one here.

I've repeatedly ranted here about ignorant twits. Ignorance is a plague on society, and it's at its worst when it's willful ignorance - that is, when you have a person who knows nothing about a subject, and who refuses to be bothered with something as trivial and useless about learning about it before they open their stupid mouths.

We've got an amazing, truly amazing, example of this in the US congress right now.
There's a "debate" going on about something called the American Community Survey, or the
ACS for short. The ACS is a regular survey performed by the Census administration, which
measures a wide range of statistics related to economics.

A group of Republicans are trying to eliminate the ACS. Why? well, let's put that question aside. And let's also leave aside, for the moment, whether the survey is important or not. You can, honestly, put together an argument that the ACS isn't worth doing, that it doesn't measure the right things, that the value of the information gathered doesn't measure up to the cost, that it's intrusive, that it violates the privacy of the survey targets. But let's not even bother with any of that.

Members of congress are arguing that the survey should be eliminated, and they're claiming that the reason why is because the survey is unscientific. According to Daniel Webster, a representative from the state of Florida:

We’re spending $70 per person to fill this out. That’s just not cost effective, especially since in the end this is not a scientific survey. It’s a random survey.

Note well the emphasized point there. That's the important bit.

The survey isn't cost effective, the data gathered isn't genuinely useful according to Representative Webster, because it's not a scientific survey. Why isn't it a scientific survey? Because it's random.

This is what I mean by willful ignorance. Mr. Webster doesn't understand what a survey is, or how a survey works, or what it takes to make a valid survey. He's talking out his ass, trying to kill a statistical analysis for his own political reasons without making any attempt to actually understand what it is or how it works.

Surveys are, fundamentally, about statistical sampling. Given a large population, you can create estimates about the properties of the population by looking at a representative sample of the population. For example, if you're looking at the entire population of America, you're talking about hundreds of millions of people. You can't measure, say, the employment rate of the entire population every year - there are just too many people. It's too much information - it's pretty much impossible to gather it.

But: if you can select a group of, say, 10,000 people, whose distribution matches the distribution of the wider population, then the data you gather about them will closely resemble the data about the wider population.

That's the point of a survey: find a representative sample, and take measurements of that sample. Then, with a certain probability of correctness, you can infer the properties of the entire population from the properties of the sample.

Of course, there's a catch. The key to a survey is the sample. The sample must be representative - meaning that the sample must have the same properties as the wider population of which it's a part. But the point of survey is to discover those properties! If you choose your population to match what you believe the distribution to be, then you'll bias your data towards matching that distribution. Your sample will only be representative if your beliefs about the data are correct. But that defeats the whole purpose of doing the survey.

So the scientific method of doing a survey is to be random. You don't start with any preconceived idea of what the population is like. You just randomly select people in a way that makes sure that every member of the population is equally likely to be selected. If your selection is truly random, then there's a high probability (a measurably high probability, based on the size of the sample and the size of the sampled population) that the sample will be representative.

Scientific sampling is always random.

So Mr. Webster's statement could be rephrased more correctly as the following contradiction: "This is not a scientific survey, because this is a scientific survey". But Mr. Webster doesn't know that what he said is a stupid contradiction. Because he doesn't care.

15 responses so far

Stupid Politician Tricks; aka Averages Unfairly Biased against Moronic Conclusions

May 13 2011 Published by under Bad Economics, Bad Statistics

In the news lately, there've been a few particularly egregious examples of bad math. One that really ticked me off came from Alan Simpson. Simpson is one of the two co-chairs of a presidential comission that was asked to come up with a proposal for how to handle the federal budget deficit.

The proposal that his comission claimed that social security was one of the big problems in the budget. It really isn't - it requires extremely creative accounting combined with several blatant lies to make it into part of the budget problem. (At the moment, social security is operating in surplus: it recieves more money in taxes each year than it pays out.)

Simpson has claimed that social security must be cut if we're going to fix the budget deficit. As part of his attempt to defend his proposed cuts, he said the following about social security:

It was never intended as a retirement program. It was set up in ‘37 and ‘38 to take care of people who were in distress -- ditch diggers, wage earners -- it was to give them 43 percent of the replacement rate of their wages. The life expectancy was 63. That’s why they set retirement age at 65

When I first heard that he'd said that, my immediate reaction was "that miserable fucking liar". Because there are only two possible interpretations of that statement. Either the guy is a malicious liar, or he's cosmically stupid and ill-informed. I was willing to accept that he's a moron, but given that he spent a couple of years on the deficit commission, I couldn't believe that he didn't understand anything about how social security works.

I was wrong.

In an interview after that astonishing quote, a reported pointed out that the overall life expectancy was 63 - but that the life expectancy for people who lived to be 65 actually had a life expectancy of 79 years. You see, the life expectancy figures are pushed down by people who die young. Especially when you realize that social security start at a time when the people collecting it grew up without antibiotics, there were a whole lot of people who died very young - which bias the age downwards. Simpson's
response to this?

If you’re telling me that a guy who got to be 65 in 1940 -- that all of them lived to be 77 -- that is just not correct. Just because a guy gets to be 65, he’s gonna live to be 77? Hell, that’s my genre. That’s not true.

So yeah.. He's really stupid. Usually, when it comes to politicians, my bias is to assume malice before ignorance. They spend so much of their time repeating lies - lying is pretty much their entire job. But Simpson is an extremely proud, arrogant man. If he had any clue of how unbelievably stupid he sounded, he wouldn't have said that. He'd have made up some other lie that made him look less stupid. He's got too much ego to deliberately look like a credulous drooling cretin.

So my conclusion is: He really doesn't understand that if the overall average life expectancy for a set of people is 63, that the life expectancy of the subset people who live to be 63 going to be significantly higher than 63.

Just to hammer in how stupid it is, let's look at a trivial example. Let's look at a group of five people, with an average life expectancy of 62 years.

One died when he was 12. What's the average age at death of the rest of them to make the overall average life expectancy was 62 years?

\frac{4x + 12}{5} = 62, x = 74

.

So in this particular group of people with a life expectancy of 62 years, the pool of people who live to be 20 has a life expectancy of 74 years.

It doesn't take much math at all to see how much of a moron Simpson is. It should be completely obvious: some people die young, and the fact that they die young affects the average.

Another way of saying it, which makes it pretty obvious how stupid Simpson is: if you live to be 65, you can be pretty sure that you'll live to be at least 65, and you've got a darn good chance of living to be 66.

It's incredibly depressing to realize that the report co-signed by this ignorant, moronic jackass is widely accepted by politicians and influential journalists as a credible, honest, informed analysis of the deficit problem and how to solve it. The people who wrote the report are incapable of comprehending the kind of simple arithmetic that's needed to see how stupid Simpson's statement was.

26 responses so far

Electoral Rubbish

Sep 30 2010 Published by under Bad Math, Bad Statistics

And now, for your entertainment, a bad math quickie.

I live in New York. 'round here, we've got a somewhat peculiar feature of how we run our elections. A single candidate can run for office on behalf of multiple parties. If they do, they appear on the ballot in multiple places - one ballot line for each party that they represent. When votes are tallied, if the candidate names for two different ballot lines match exactly, then the votes for those two lines are combined.

The theory behind this is that it allows people to say a bit more with their votes. If you want to vote for the democratic candidate, but you also want to express you preferences for policies more liberal than those of the democratic party platform, you can vote for the democrat, but do it on the liberal party line instead of the democratic party line.

In practice, what this means is that we've got lots of patronage parties - that is, lots of small parties which were set up by a small group of people as a way of making money by, essentially, selling their ballot line.

One thing we hear, election after election, is how terribly important these phony parties are. This year, we keep on hearing, over and over, how no Republican has won a statewide election since 1975 without the backing of the Conservative party! Therefore, winning the backing of the Conservative party is so very, very important!

This is, alas, a classic example of the old problem: correlation does not imply causation. The Republicans don't lose elections because they don't have the backing of the Conservative party: the Conservative party always backs the republican candidate unless it's completely clear that they're going to lose.

Continue Reading »

11 responses so far

Iterative Hockey Stick Analysis? Gimme a break!

Apr 29 2010 Published by under Bad Statistics

This past weekend, my friend Orac sent me a link to an interesting piece
of bad math. One of Orac's big interest is vaccination and
anti-vaccinationists. The piece is a newsletter by a group calling itself the "Sound Choice
Pharmaceutical Institute" (SCPI), which purports to show a link
between vaccinations and autism. But instead of the usual anti-vac rubbish about
thimerosol, they claim that "residual human DNA contamintants from aborted human fetal cells"
causes autism.

Among others, Orac already covered the nonsense
of that from a biological/medical
perspective. What he didn't do, and why he forwarded this newsletter to me, is because
the basis of their argument is that they discovered key change points in the
autism rate that correlate perfectly with the introduction of various vaccines.

In fact, they claim to have discovered three different inflection points:

  1. 1979, the year that the MMR 2 vaccine was approved in the US;
  2. 1988, the year that a 2nd dose of the MMR 2 was added to the recommended vaccination
    schedule; and
  3. 1995, the year that the chickenpox vaccine was approved in the US.

They claim to have discovered these inflection points using "iterative hockey stick analysis".

Continue Reading »

28 responses so far

Shameful Innumeracy in the New York Times

Nov 17 2009 Published by under Bad Statistics

I've been writing this blog for a long time - nearly four years. You'd think that
after all of the bad math I've written about, I must have reached the point where
I wouldn't be surprised at the sheer innumeracy of most people - even most supposedly
educated people. But alas for me, I'm a hopeless idealist. I just never quite
manage to absorb how clueless the average person is.

Today in the New York Times, there's an editorial which talks about
the difficulties faced by the children of immigrants. In the course of
their argument, they describe what they claim is the difference between
the academic performance of native-born versus immigrant children:

Whereas native-born children's language skills follow a bell
curve, immigrants' children were crowded in the lower ranks: More than
three-quarters of the sample scored below the 85th percentile in English
proficiency.

Scoring in the 85th percentile on a test means that you did better on that
test than 85 percent of the people who took it. So for the population as a
whole
, 85% of the people who took it scored below the 85th percentile -
by definition. So, if the immigrant population were perfectly matched
with the population as a whole, then you'd expect more than 3/4s the
score below the 85th percentile.

As they reported it, the most reasonable conclusion would be that on the
whole, immigrant children do better than native-born children! The
population of test takers consists of native-born children and immigrant
children. (There's no third option - if you're going to school here, either
you were born here, or you weren't.) If 3/4s of immigrant children are scoring
85th percentile or below, then that means that more than 85% of
the non-immigrant children are scoring below 85th percentile.

I have no idea where they're getting their data. Nor do I have any idea of
what they thought they were saying. But what they actually said is a
mind-boggling stupid thing, and I can't imagine how anyone who had the most
cursory understanding of what it actually meant would miss the fact that
the statistic doesn't in any way, shape, or form support the statement it's
attached to.

The people who write the editorials for the New York Times don't even
know what percentiles mean. It's appalling. It's worse that appalling - it's
an absolute disgrace.

40 responses so far

The Chevy Volt Gets 230 mpg? Only if you use bad math.

Aug 11 2009 Published by under Bad Statistics

Here's a quick bit of obnoxious bad math. I saw this myself in a link to an AP article via Salon.com, and a reader sent me a link
to the same story via CNN. It's yet another example of what I call a metric error: that is, the use of a measurement in a way that makes it appear to mean something very different than what it really means.

Here's the story. Chevy is coming out with a very cool new car, the Volt. It's
a hybrid with massive batteries. It plugs in to your household electricity when you're home to charge its batteries. It operates as an electric car until its batteries start to get low, and then it starts running a small gas motor to power a generator. It's a very cool idea. I'm honestly excited about cars like the volt - and Google helped develop the technology behind it, which biases me even more in its favor. So you'd expect me to be very supportive of the hype around it, right? I wish I could. But GM has decided that the best way to promote it is to use bad math to tell lies to make it look even better than it really is.

Chevy has announced that for city driving, the Volt will get gas mileage of 230 miles per gallon.

That's nonsense. Pure, utter rubbish.

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154 responses so far

Bill O'Reilly on Life Expectancy: Dumbest Man on Earth?

Jul 28 2009 Published by under Bad Economics, Bad Statistics

An alert reader just sent me, via "Media Matters", the single dumbest real-life
video clip that I have ever seen. In case you've been living under a rock, Bill O'Reilly is
a conservative radio and TV talk-show host. He's known for doing a lot of really obnoxious
things, ranging from sexually harassing at least one female employee, to sending some of
his employees to stalk people who he doesn't like, to shutting off the microphones of
guests on his show if he's losing an argument. In short, he's a loudmouthed asshole who
gets off on bullying people.

But that's just background. As a conservative commentator, he's been going off on
the evils of Obama's supposedly socialist healthcare reform. That's frequently
taken the form of talking about how horrible medical care is under Canada's
socialized health system. One of his viewers wrote in to him about this. And
the insanity follows.

The question came from a viewer named Peter from Victoria, BC, who asked: "Has anyone noticed
that life expectancy in Canada under our health system is higher than the USA?"

Bill's response:" Well, that's to be expected Peter, because we have 10 times
as many people as you do. That translates to 10 times as many accidents,
crimes, down the line." Delivered, of course, in BillO's trademark patronizing
style.

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70 responses so far

More Deceptive Graphs: Scales Matter

Apr 06 2009 Published by under Bad Statistics

Yet More Deceptive Graphs

As you've probably heard, there was a horrible incident in Pittsburgh this weekend, in
which a crazed white supremacist who believed that Obama was coming to take his guns shot and
killed three policemen. Markos Moulitsas, of Daily Kos, pointed out lunatics like this shooter
are acting on conspiracy theories that are being relentlessly promoted by the likes of Glen
Beck and Michelle Bachman. It's not an unreasonable thing to point out, given the amount of
time that Beck and Bachman have spent lately talking about the impending socialist/fascist
crackdowns that will require a revolutionary response from all right-thinking patriotic
citizens.

Now, you may think that Kos is an idiot. In fact, even though we agree on many
political issues, I think that Kos is an idiot. I (obviously from what
I wrote above) happen to agree with the basic hypothesis that if you tell
people that the government is going to come and get that and that they need to
defend themselves, that some people are going to believe that the government is
coming to get them and that they need to defend themselves. But the way
that Kos responded was disgusting; it was latching on to a tragic event in
a shallow, snide, heartless way.

But whether you think Kos is an ass ore not isn't the point. Regardless of your opinion of
the man, there's no arguing the fact that he's created a website that draws a really
astonishing amount of traffic, and has become a nexus for many activists on the political
left.

And that, in turn, naturally draws hatred and mockery from the political right. Because,
you see, no one who disagrees with those fine patriotic folks could possibly be an
honest, serious person. They must be a bunch of scheming bastards, obviously.

So, when Kos came out bitching about how the rantings of various crazies really do
have a connection to the actions of people like the Pittsburgh killer, naturally it couldn't be that he actually believed that people ranting about how the President is
creating a fascistic tyranny that's going to come take all of your guns could actually
inspire a crazy person to believe that the President creating a fascistic tyranny that was going to come and take away his guns. No, that couldn't be. He must be up to something - like trawling for hits!

Which, finally, brings us to our topic.

A conservative blogger named Moe Lane posted his theory about why Kos spoke out about the Pittsburgh shooter. It's because his pageviews have declined so much. But, of course, it wouldn't be good enough to just say that DKos pageviews are down - he's got to show that it's specific to those dirty liberals. So he produces two graphs - one for DKos, and one for RedState, a major conservative site. Here are his graphs; DKos first, Redstate second:

dkos-300x244.jpg
rs-300x244.jpg

A quick glance shows that both had a huge spike right around the elections, and then they
dropped off pretty dramatically. Then both had a slow upward trend. But the RedState trend
looks a lot steeper.

Continue Reading »

16 responses so far

Financial Morons, and Quadratics vs. Linears

Feb 16 2009 Published by under Bad Economics, Bad Statistics

I wasn't going to write about this, because I really don't have much to add. But people keep mailing it to me, so in order to shut you all up, I'll chip in.

As everyone knows by now, we're in the midst of a really horrible
financial disaster. I've argued in the past on this blog that the root cause of the entire disaster is pure, simple stupidity on the part of people in the financial business. People gave out mortgages that any
sane rational person would have considered ridiculous. And then they built huge, elaborate financial structures on top of those mortgages, pretending that by somehow piling layer upon layer, loan upon loan, that
they were somehow creating something that could be considered real wealth.

bankcap6-1024x747.jpg

They gave themselves bonuses that boggled the mind. Even after the whole ridiculous system came tumbling down, they continue to give themselves ridiculous bonuses. Insane bonuses. They've been writing themselves checks for millions of dollars to continue to operate their
businesses - even after taking billions of dollars in loans from the government to prevent them from going out of business. I consider
this to be downright criminal. But even if it's not criminal, it's
incredibly stupid. The very people who ran those firms right to the edge of bankruptcy, who nearly took down our entire financial system
are being rewarded. Not only are they being allowed to continue
to rut the businesses that they pretty much destroyed, but they've
been paying themselves an astonishing amount of money to do it. And now they're complaining bitterly about the fact that the government
wants to limit them to a paltry half-million dollars of salary per year.

They argue that they must be allowed to earn more than that. Because after all, the people who run those businesses are special. They're "the best and the brightest". They're
extra-smart. No one else could possibly run those businesses. We can't rely on anyone who'd accept a puny half-mil - they won't be smart enough. They don't have the special knowledge of the business that these people do.

There's one minor problem with that argument: it doesn't work. A couple of weeks ago, some idiot at JP Morgan circulated a chart that was supposed to summarize just how bad the financial disaster has been. The chart circulated for a couple of weeks - bounced from mailbox to mailbox, sent from one financial genius to another.

Only the chart was blatantly, obviously, trivially wrong, and anyone who had the slightest damned clue of the assets those businesses managed - i.e., the kind of thing that the idiot who drew the chart was supposed to know - should have been able to tell at a glance how wrong it was. But they didn't. In fact, the damned thing didn't stop circulating until (of all people) Bob Cringely
flamed it. Go look at the chart - it's up at the top of this post.

Continue Reading »

50 responses so far

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