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Category: Statistics

The general theory, methods, and philosophy of the Science of Guessing What Is.

December 24, 2007 | No comments

Two differences in perception between global cooling and global warming

As is well known by now, a passel of climatologists in the 1970s, including such personalities as Stephen “It’s OK to Exaggerate To Get People To Believe” Schneider, tried to get the world excited about the possibility, and the dire consequences, of global cooling.

From the 1940s to near the end of the 1970s, the global mean temperature did indeed trend downwards. Using this data as a start, and from the argument that any change in climate is bad, and anything that is bad must be somebody’s fault, Schneider and others began to warn that an ice age was imminent, and that it was mainly our fault.

The causes of this global cooling were said to be due to two main things: orbital forcing and an increase in particulate matter—aerosols—in the atmosphere. The orbital forcing—a fancy term meaning changes in the earth’s distance and orientation to the sun, and the consequent alterations in the amount of solar energy we get as a result of these changes—was, as I hope is plain, nobody’s fault, and because of that, it excited very little interest.

But the second cause had some meat behind it; because, do you see, aerosols can be made by people. Drive your car, manufacture oil, smelt some iron, even breath and you are adding aerosols to the atmosphere. Some of these particles, if they diffuse to the right part of the atmosphere, will reflect direct sunshine back into space, depriving us of its beneficial warming effects. Other aerosols will gather water around them and form clouds, which both reflect direct radiation and capture outgoing radiation—clouds both cool and warm, and the overall effect was largely unknown. Aerosols don’t hang around in the air forever. Since they are heavy, over time they will fall or wash out. It’s also hard to do too much to reduce the man-made aerosol burden of the atmosphere; except the obvious and easy things, like install cleaner smoke stacks.

Pause during the 1980s when nothing much happened to the climate.

Continue reading “Two differences in perception between global cooling and global warming”

December 20, 2007 | No comments

Can increasing fuel economy standards result in more gas consumed?


Congress recently passed an increase in fuel efficiency standards for cars, from 25 MPG to 35 MPG, a 40% jump. So you would expect that, when this law goes into force, gasoline usage will go down. That’s what various congresspersons and “environmentalists” are arguing, anyway.

Unintended consequences

Now, the mandated increase is a very large change, and complying with the law is probably beyond current engineering capabilities. That is, automotive engineers will have a difficult time implementing these standards in the time alloted, unless they do the one easy thing available to them, which is to make cars lighter. Lighter cars get higher gas mileages.

Making cars lighter is not hard. You simply take things out of heavy cars or make smaller cars. Problem solved!

Except smaller and lighter cars, all other things being equal, fare far worse in crashes. People know this, and tend to buy a larger vehicle instead. That is, confronted with a choice of a small, more dangerous, car, they will more likely buy a larger SUV or a truck.

Trucks and SUVs do not have to comply with the higher gas mileage requirements. Mileage for these larger vehicles is about 15 MPG (average of city and highway driving).

So instead of buying a safer car that now gets the required 25 MPG, people will be more likely to buy vehicles that are, on average, 60% less efficient!

Thus, more gas will be used than before the higher standards were in place.

Of course, I cannot prove that my scenario is certain to happen, but it is at least not impossible, and even somewhat likely. If I am right, this will be yet another example of good intentions gone bad.

December 6, 2007 | 2 Comments

Hurricanes have not increased in the North Atlantic

My paper on this subject will finally appear in the Journal of Climate soon. You can see it’s status (temporarily, anyway) at this link.

You can download the paper here.

The gist is that the evidence shows that hurricanes have not increased in either number of intensity in the North Atlantic. I’ve only used data through 2006; which is to say, not this year’s. But if I were to, then, since the number and intensity of storms this past year were nothing special, the evidence would be even more conclusive that not much is going on.

Now, I did find that there were some changes in certain characteristics of North Atlantic storms. There is some evidence that the probability that strong (what are called Category 4 or 5) storms evolving from ordinary hurricanes has increased. But, there has also been an increase in storms not reaching hurricane level. Which is to say, that the only clear signal is that there has been an increase in the variability of intensity of tropical cyclones.

Of course, I do not say why this increase has happened. Well, I suggest why it has: changes in instrumentation quality and frequency since the late 1960s (which is when satellites first went up, allowing us to finally observe better). This is in line with what others, like Chris Landsea at the Hurricane Center, have found.

I also have done the same set of models of global hurricanes. I found the same thing. I’m scheduled to give a talk on this at the American Meteorological Society’s annual meeting in January 2008 in New Orleans. That paper is here.


How to Exaggerate Your Results: Case study #1

In the Tuesday, 6 November 2007 edition of the Wall Street Journal, Pfizer took out a full-page ad encouraging people to “Ask your doctor” about Lipitor, a drug which claims to lower your “risk” of a heart attack (p. A13). In enormous bold print are the words:

Lipitor reduces risk of heart attack by 36%*.


Following that asterisk on the 36% leads to something interesting:

*That means in a large clinical study, 3% of patients taking a sugar pill or placebo had a heart attack compared to 2% of patients taking Lipitor.


Congratulations, Pfizer! This ad scores a solid 7 on the Statistical Deception Scale.

First, if you take Lipitor your risk is only lowered by a relative amount, from an already low 2% to a slightly lower 1%. Your real risk is only lowered by 1%. There is a world of difference between that 36% and 1%, and the ad did say, sort of, that the risk was relatively lowered, not lowered absolutely, so it wasn’t terribly deceptive at that point. It’s true, too, that some people might think to themselves, “Ah, any lowering is good, even if it’s only 1%.” More on that sentiment in a moment.

But what most people won’t see, or will ignore, are the smaller words under the bold headline, which say that your risk is lowered “If you have risk factors such as family history, high blood pressure, age, low HDL (‘good’ cholesterol) or smoking.” Aha! This is what ups Pfizer’s ranking on the deception scale.

Thus, in order to get the 1% reduction it turns out that you have to be in a pretty high risk group to begin with; namely, those with “multiple” risk factors. How many risk factors do you have to have before you can hope for the reduction? Two? Three? The ad doesn’t say. Maybe you need all five before you can hope for the reduction. That is the most likely reading of the ad.

What if you don’t have all five? We might guess that your absolute risk reduction is either zero or negligible. We guess this because if people could reduce their risk generally, without belonging to a highly selective group, that Pfizer would have boasted of this. They did not so boast, so etc. etc.

Back to the “any lowering is good” sentiment. On the page opposite the pictures, Pfizer has quite a long list called “POSSIBLE SIDE EFFECTS OF LIPITOR”. Among these new risks are, muscle problems, kidney “problems” or even failure, liver problems, nausea, vomiting, brown colored urine, tiredness, yellowing eyes (!), rash, gas, and others. The key words are these:

Fewer than 3 people out of 100 stopped taking LIPITOR because of side effects.

Well, must I point out that 3 out of 100 is 3%, which is more—67% more!—than the 2% (in the high risk group) who will have a heart attack, and 200% more than the 1% (or so) of the “regular” people who will have a heart attack? I guess I don’t need to. Of course, we can’t figure out, given only the data that Pfizer provides in the ad, what the actual chance is that a regular person will have a heart attack or suffer “side” effects. But there is enough information provided that should severely limit enthusiasm for this drug.

The advertisement also pictures Robert Jarvik, inventor of the “Jarvik artificial heart”, badly in need of a haircut, standing in front of a colorful heart-like object. But he is a celebrity doctor, and isn’t that all you really need to know?