quote:The intense interest about climate change comes as some 500 climate scientists gather in Paris this week to put the final touches on a United Nations report on how warming, as a result of a growing concentration of heat-trapping gases in the atmosphere, is likely to affect sea levels.
They agree sea levels will rise, but not on how much. Whatever the report says when it comes out at week's end, it is likely to influence the climate debate in Congress.
How will the numbers for the report be finalized? Do scientists get together all their numbers and...I dunno, average them out? Do they debate the merits of this or that, and whoever is the better speaker, or is better looking, or whoever buys the most liquor for the rest of the conference wins?
j/k. You know, in case you decide to flame me or something.
That said, it's this kind of thing that bugs me a little about the scientific community. 500 scientists will put out a report, apparently giving a specific quantitative measure of X-- and some of those contributing to the formulation may not even agree that X is REALLY X.
So how does getting consensus with quantitative data really happen? Especially with so charged a topic as rising sea levels?
EDIT: The phrase "bugs me about" is inarticulate. I meant to say, "wonder about intensely for the next two minutes."
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Scott, Can you think of another form the report might take other than saying "We think that the sea levels will rise exactly X inches."? I doubt pretty strongly that this is going to be the form it will take.
I think what's bugging you is a chimaera of your own devising and not indicative of the reality of the situation.
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Another point is that what the popular science reports as "two scientists disagree" is usually nothing more than "I measure with method A and get X +- Y, and he gets X' +- Y' using method B." This does not imply that either scientist thinks method A or B is superior, or that the other result is incorrect. Generally the measurements will agree within errors; we're not talking orders of magnitude here. In any case, there are well-known mathematical methods for properly averaging such numbers; it's not a question of taking a vote.
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I read an article on cnn.com that said there are many climate scientists outraged by the reports that will presented at this conference. Specifically so because it does not take into account the recent problems with ice sheets in Greenland and Antarctica. Those incidents are mentioned only in footnote.
So, supposedly, the report will say that seas will rise from 3-23 inches, while those who are factoring in the ice sheet problem are predicting 25-50 inches. That's a hell of a swing.
It seems, though, that the report has a deadline that must be met, and the new scientific data adjusted for the ice sheets has not yet been put through the rigors of scientific inspection.
Either way, it seems the report will be flawed, just because it doesn't scientifically account for the new data.
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quote:So, supposedly, the report will say that seas will rise from 3-23 inches, while those who are factoring in the ice sheet problem are predicting 25-50 inches.
Apparently, some are talking orders of magnitude.
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I didn't have a problem with the article. I imagine that the report will reflect the uncertainty. If they do roll some dice or do anything else to try o fix an exact number with so much uncertainty, then let us know and I'll get bugged about it too. Posts: 2392 | Registered: Sep 2005
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Scott, My fault for expecting you to be respectful when the answer to you question is something you don't want to hear.
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Is there anyone who knows what they are talking about that can answer Scott's question? I'll bet CT would know about how to report scientific conclusions made by a collective.
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Have YOU ever seen Kymaera? I mean, she is one hawt super-babe.
I do not understand why she shed her skin and got pupils. She looked so much more foine with the net, and the seashells, and the blue skin...
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quote:Another point is that what the popular science reports as "two scientists disagree" is usually nothing more than "I measure with method A and get X +- Y, and he gets X' +- Y' using method B." This does not imply that either scientist thinks method A or B is superior, or that the other result is incorrect. Generally the measurements will agree within errors; we're not talking orders of magnitude here. In any case, there are well-known mathematical methods for properly averaging such numbers; it's not a question of taking a vote.
If there is a system configured to make diverse answers jibe, and the scientific community is kosher with that, fantastic. That's what I wanted to know.
(Also want to find out if such things are usually divulged in a paper...)
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posted
I've already answered Scott's question. So has FC.
In matters such as this, there are a number of approaches that are taken. One of the most common is to give a range that the quantitative value would theoretically fall in. Another is to present the different theories at work with their differing predictions in a summary section with separate sections laying out the details for each.
What they don't do as far as I've ever been aware is to try to come up with one certain number when no such certainty exists.
Having such an unreasonable thing as a starting assumption suggests to me that the person has a pretty large axe to grind.
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quote:So, supposedly, the report will say that seas will rise from 3-23 inches, while those who are factoring in the ice sheet problem are predicting 25-50 inches.
Apparently, some are talking orders of magnitude.
That's a factor 3, only one-half of an order of magnitude.
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And yes. That is me holding the axe. The dude in front, with the skull necklace, not the whiney, earth-sucking, lizard cavorting short guy in the back.
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In algorithmic analysis, we always used base 2 for orders of magnitude.
Of course, with only two things to compare, "order of magnitude" is adding extra complexity and no additional information - just give the factor.
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KoM, That would only be valid if we were talking about two methods of analysis, rather than two families of method of analysis.
You can't assume that all the methods from the first part average out to 13. Some may have a range from 3 to 5 inches.
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Dag, In physical measurement, I've never known an order of magnitude to be anything other than base 10.
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quote:Dag, In physical measurement, I've never known an order of magnitude to be anything other than base 10.
Likely. I've spent far more time in the software/EE world than in activities involving physical measurement.
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Yes, but by that logic you might as well say that 23 to 25 is 10%. Without additional information, you're going to have to go for the straightforward average.
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But Mr. Squicky, the low end of 3 matches with the low end of 25, not 30--hence not quite an order of magnitude, while the big end of 23 is merely just under 1/2 the big end of 50.
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I disagree. When we're talking about a collection of measuring methods that have such a wide range, I think it is reasonable to assume that at least one method is going to have a relatively low average value.
This doesn't have to be that case and it may be that some methods have a much wider range, giving us both the lows and the highs, but this seems much less likely.
The goal is not to play some sort of numbers game but to assess what is likely to be true, and what you are suggesting, that the measurings can be assumed to have ranges that average out to 13 is very, very unlikely to be true.
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dan, But, as I said, we are not dealing with comparing two methods with ranges 2-23 and 25-50, but rather two families of methods that somehow have these ranges of predicted values. When we are talking about an order of magnitude, we are talking about comparing individual methods and not the families as a whole.
While it is not certain that two separate methods exist that have an order of magnitude between their range of estimated values, it is a reasonable suggestion.
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aspectre, That's for reconciling differences in statistical surveys of a population, not for reconciling differing predictions from theoretically separate models. It's not relevant here.
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From what I understand of meta-analysis, it's primarily used in studying statistics. How can it be used to build consensus on forecasted/projected information?
And I want to make sure I'm clear this time, so the conversation doesn't get bogged down in whether or not I'm arguing against science, scientists, or global warming:
I like science.
I like scientists.
I accept that global warming is occurring, and whether or not there is a human factor to it does not matter to the question of whether we should cut back on energy consumption: we should, and I have.
I'm curious as to how scientists with differing viewpoints mesh those together to make a report that will influence politics and laws.
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I must disagree. (Incidentally, this rather reinforces my original point: Here are two people, at least one a scientist from outside the field, unable to agree on what kind of range is probably being given! (I've forgotten what your work is, Squicky - I seem to recall some kind of science, but I don't remember what field.)) Now, if I were giving a range for a physical quantity, then generally it would be symmetric; my high end would be as likely as my low end. If that's not true, then just giving the range is not actually very informative and you shouldn't do it. Therefore, in my experience, taking a simple average of the upper and lower bounds is very likely to give you the most probable result. And I do not quite appreciate your suggestion that I am playing numbers games.
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KoM, I'm not talking about averages here. I'm talking about whether it is reasonable to assume that there is at least one method from the one family predict values an order of magnitude different from at least one method from the other.
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I'm a psychologist, one of whose areas of study heavily involves game theory.
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quote:Originally posted by MrSquicky: KoM, I'm not talking about averages here. I'm talking about whether it is reasonable to assume that there is at least one method from the one family predicting values an order of magnitude different from at least one method from the other.
Fine, but that's not a very interesting question, is it? The whole point of having more than one analysis is so you can average them. In this case, the new family takes into account additional data which, presumably, would strongly increase the predictions of the old family, so you shouldn't do the comparison like that in any case.
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quote:The whole point of having more than one analysis is so you can average them.
I don't see why that would be the case here. You've got more than one analysis because you are dealing with different theoretical projective models. There's nothing here that would suggest averaging their predictions for any reason.
If someone has a model that say something will be 4 and someone else has a model that says it will be 10, this doesn't suggest that the real value will be 7. Rather, it is that if the first person's model is correct it will be 4 and if the second person's is correct it will be 10. There is no valid way of combining these predictions.
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I rephrase. If the numbers can be combined at all, then averaging is the correct way to do it. If the numbers are, as you suggest, incompatible, then no range should have been given, because it is misleading.
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The range is given to set out an area of potential effect. For a more valid perspective, you've got the detailed report, but for the summary, which is all that most non-scientists are going to have anything to do with, you need some easy to understand numbers.
Take, for example, disaster planning/prediction in a discrete scenario case. You run your different scenarios and can give a projected range of effect for each. Best case is such and such, worst case is something else. When you've got a ton of different scenarios where the predictions spread across an entire range, offering the area of potential effect as a range in this manner makes a deal of sense, when presenting it to a non-sophisticated audience.
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I find it funny those talking about orders of magnitude.
One group is advocating a "low" amount of 1/4 of a foot. The other group is advocating a "low" of two feet.
In the best case scenario of the first group, things aren't so bad.
In the best case scenario of the second group, we're looking at losing a great deal of our coastal cities to flooding.
In the worst case scenario of the first group, you're looking at the best case of the second group. That's a pretty extreme difference.
In the worst case scenario of the second group, the oceans rise more than four feet. That would cause utter global devestation.
You're arguing about orders of magnitude? It's like the joke about the mathematician and the hot air balloon.
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You've never heard that joke? Here's the abridged version:
A guy is flying in a hot air balloon and gets lost in the fog. Drifting down, he sees a mathematician on a hilltop. He shouts down, "Where am I?"
The mathematician responds, "You're in a hot air balloon!"
<insert polite laughter>
I know it's an old, tired joke. But it's meant to show that sometimes mathematicians can get caught up in the details and particulars and lose the big picture.
My point was - who cares if it's an order of magnitude or not, it's an incredibly geologically significant difference in estimates.
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quote:Originally posted by FlyingCow: You've never heard that joke? Here's the abridged version:
A guy is flying in a hot air balloon and gets lost in the fog. Drifting down, he sees a mathematician on a hilltop. He shouts down, "Where am I?"
The mathematician responds, "You're in a hot air balloon!"
<insert polite laughter>
I know it's an old, tired joke. But it's meant to show that sometimes mathematicians can get caught up in the details and particulars and lose the big picture.
My point was - who cares if it's an order of magnitude or not, it's an incredibly geologically significant difference in estimates.
Point taken, and thanks for simply explaining the application before I had to apply my own brain power to the question. Posts: 14316 | Registered: Jul 2005
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