Category: Geek stuff

If it involves physics, math, computer science, electronics or has general geek cachet, this is the place for it.

Doctors and conditional probabilities

While it is not surprising, it is worrisome that doctors have trouble with statistics, particularly conditional probabilities. 25 German doctors were asked about the following situation. It is clearly a tricky question, but it is surely a type of question that doctors are exposed to constantly:

The probability that one of these women has breast cancer is 0.8 percent. If a woman has breast cancer, the probability is 90 percent that she will have a positive mammogram. If a woman does not have breast cancer, the probability is 7 percent that she will still have a positive mammogram. Imagine a woman who has a positive mammogram. What is the probability that she actually has breast cancer?

The results of this small trial were not encouraging:

[The] estimates whipsawed from 1 percent to 90 percent. Eight of them thought the chances were 10 percent or less, 8 more said 90 percent, and the remaining 8 guessed somewhere between 50 and 80 percent. Imagine how upsetting it would be as a patient to hear such divergent opinions.

As for the American doctors, 95 out of 100 estimated the woman’s probability of having breast cancer to be somewhere around 75 percent.

The right answer is 9 percent.

You would think that this sort of quantitative analysis would play an important role in the medical profession. I am certain that a great many people around the world have received inappropriate treatment or taken unnecessary risks because doctors have failed to properly apply Bayes’ Theorem. Indeed, false positives in medical tests are a very commonly used example of where medical statistics can be confusing. It is also a problem for biometric security protocols, useful for filtering spam email, and a common source of general statistical errors.

The proper remedy for this is probably to provide doctors with simple-to-use tools that allow them to go from data of the kind in the original question to a correct analysis of probabilities. The first linked article also provides a good example of a more intuitive way to think about conditional probabilities.

Psychology and romantic attraction

The psychology course I have been following features a Valentine’s Day lecture about love. Mostly, it is about what seems to make people attracted to one another, as demonstrated by psychological experiments.

Professor Peter Salovey, the guest lecturer, argues that we have empirical evidence for seven major causes of attraction. Three of them are fairly obvious, but very demonstrably important. The next four are more subtle, but are also supported by experimental investigation.

The big three:

  1. Proximity – we are more likely to get romantically involved with those who we live near
  2. Familiarity – the more we see a person, the more likely we are to get involved with them
  3. Similarity – apparently, opposites do not attract

The practical utility of this is obvious, for those looking for a romantic partner. Move to an area with people who you find attractive, and participate in social events with like-minded people, so as to improve your odds of being similar to and familiar with attractive people.

The more subtle four:

  1. Competence – the people who we like the very best are those that strike us as highly competent, but who make some sort of humanizing blunder
  2. Physical attractiveness – many people underestimate how important a factor this is for themselves
  3. An increasingly positive view – if someone seems to be warming towards us, it is highly interesting
  4. Mis-attribution of good feelings – we feel good or excited for a reason unrelated to a person, but wrongly attribute the feeling to them

These all also suggest dating strategies. The last two seem particularly easy to manipulate. It is also worth noting that we are most attracted to people who seem to be very exclusive in their choice of partners, but who we do not expect to be picky or difficult in our case. That may not be enough to constitute a Revolutionary New Dating Paradigm, but it might be helpful for some people.

Climate change and the seal hunt

Over the weekend, I found myself wondering about the relative impact of Canada’s extremely controversial seal hunt and climate change, when it comes to the prospects for Grey Seals and Harp Seals.

Given that it seems highly likely that climate change will eventually eliminate summer sea ice, and given that creatures including seals seem to be critically dependent on sea ice, it does seem possible that climate change will render these seal species extinct, eventually, or will sharply curtail their numbers.

Stage one of a comparative analysis would be developing an estimate of how many seals would have lived between the present and the non-human-induced extinction of the species. They could potentially endure until the end of the carbon cycle, or until the sun expands into a red giant. More plausibly, they might exist in large numbers until the next time natural climate change produces a world too hot to include Arctic sea ice.

If we had an estimate of how far off that probably is, and an estimate of the mean number of seals that would be alive across that span, then we can estimate how many seals would be lost if humanity eliminates summer sea ice and, by extension, wipes out or sharply curtails the number of these animals in the wild.

It is possible to imagine a chart showing seal population year by year, extending far into the future. There could be one shaded segment showing the projected seal population in the absence of human intervention, and others showing possible population crashes resulting from anthropogenic climate change. A third shaded area could show the number of seals taken annually by hunters. The relative area of the shaded regions would show the relative magnitude of hunting and climate change, as causes of seal mortality. If you think of all the seals that would have lived, if we hadn’t locked in the eventual disappearance of summer arctic sea ice, the number killed by hunters is probably quite small.

My suspicion is that hunting would be a tiny blip, compared with climate change. If so, the environmentalist campaign to end seal hunting seems misdirected. Even if protesters are more concerned about animal cruelty than about species sustainability, this argument seems to hold up. Surely it is cruel for the seals to suffer and slowly die off as their habitat loses the capacity to sustain them.

I think it would be well worth some serious organization producing an quantitative version of the argument above. Like ducks, it seems quite possible that seals are distracting us from the environmental issues we should really combating, or at least encouraging us to respond to those issues in a less effective way than we could.

Psychology of language learning

Continuing with the introductory psychology course I mentioned earlier, I have gotten to the section on language. A few of the things mentioned in it seem to have quite a bit of practical importance:

  • Elaborate language learning tools like flashcards are pointless, for teaching children language.
  • Pre-pubescent children are fundamentally more capable of learning languages than people beyond puberty, who will likely never be able to speak new languages without an accent.
  • Children learning two languages at once learn both just as fast as children learning only one or the other.
  • Being intelligent and social is not sufficient for a being to be capable of learning language. For instance, mutations in certain human genes can prevent people from ever being able to speak or understand language.
  • There is a strong genetic component in the ability people have to learn languages; those with parents skilled in the task are likely to be skilled as well.

The take-home message seems to be that if you want to give a child linguistic advantages, expose them to two or more useful languages as young as possible.

Back up genes from endangered species

Out in Svalbard there is a seed bank, buried in the permafrost. The idea is that it will serve as a refuge for plant species that may vanish elsewhere, perhaps because industrial monocrops (fields where only a single species is intentionally cultivated by industrial means) continue to expand as the key element of modern agriculture.

Perhaps there should be a scientific and conservational project to collect just the genes of some of the great many species our species is putting into peril: everything from primates to mycorrhizal fungi to marine bacteria. The data could be stored, and maybe put to use at some distant point where humanity at large decides that it is better to carefully revive species than to indifferently exterminate them.

For many creatures, the genes alone won’t really be enough, regardless of how good at cloning we become. An elephant or a chimp built up alone from cells would never really become and elephant or chimp as they exist today. Whether those alive now are socialized in a natural or an artificial environment, they will have had some context-sensitive socialization, which subsequently affected their mental life. It is plausible to say that elephants or chimps raised among their peers, living in the way they did thousands of years ago, will develop mentally in a manner that is profoundly different from elephants or chimps in captivity today, much less solitary cloned beings in the future. Those beings will be weird social misfit representatives of those species.

Still, it is better to have misfits than nothing at all. If there is anything human beings should really devote themselves to backing up with a cautious eye turned towards an uncertain future, it seems far more likely to be the genes of species our descendants may not be fortunate enough to know than the Hollywood movies that probably account for a significant proportion of all the world’s hard drives.

Krugman on climate economics

Nobel Prize-winning economist Paul Krugman has written an excellent introductory article on climate and environmental economics, for The New York Times: Building a Green Economy. The piece is a combination of a non-technical introduction and a kind of literature review. His basic thesis is:

In fact, once you filter out the noise generated by special-interest groups, you discover that there is widespread agreement among environmental economists that a market-based program to deal with the threat of climate change — one that limits carbon emissions by putting a price on them — can achieve large results at modest, though not trivial, cost. There is, however, much less agreement on how fast we should move, whether major conservation efforts should start almost immediately or be gradually increased over the course of many decades.

I agree that the latter disagreements exist, and I agree with Krugman that what we know about the climate system justifies aggressive action to reduce and eventually eliminate greenhouse gas emissions. In particular, the non-trivial danger of catastrophic outcomes is a strong justification for precautionary action.

The article includes a concise explanation of Pigovian taxes, of which carbon taxes are a sub-category:

What Pigou enunciated was a principle: economic activities that impose unrequited costs on other people should not always be banned, but they should be discouraged. And the right way to curb an activity, in most cases, is to put a price on it. So Pigou proposed that people who generate negative externalities should have to pay a fee reflecting the costs they impose on others — what has come to be known as a Pigovian tax. The simplest version of a Pigovian tax is an effluent fee: anyone who dumps pollutants into a river, or emits them into the air, must pay a sum proportional to the amount dumped.

Note that as discussed here before, such taxes may be technical mechanisms, but they do not eliminate the need to make ethical choices. Just because a company has been burning coal for decades doesn’t mean it has the right to continue doing so, particularly as new information on why its use is harmful comes to light. By the same token, it is not an ethically neutral choice to say that people who have enjoyed a clean river have the right for it to remain unpolluted. There are many bases on which claims can be made: historical precedent, need, prior agreements, overall welfare, etc. Economics alone cannot provide a solution.

The article also covers cap-and-trade systems, and the ways in which they are similar to and different from carbon taxes; the importance of whether permits are auctioned or not; how even strong mitigation policies would only cost 1-3% of the global domestic product; the importance of major emerging economies taking action; carbon tariffs as a way of encouraging that; the sustantial costs of inaction; the signicance of catatrophic risks (“it’s the nonnegligible probability of utter disaster that should dominate our policy analysis”); a non-mathematical discussion of discount rates; and the status and prospects of climate legislation in the United States.

In short, the article touches on a great many topics that have been discussed here previously, and generally reaches rather similar conclusions to mine and those of most of this site’s commentors. One slightly annoying thing about the piece is that is discusses temperatures using the idiotic Fahrenheit scale, but I suppose that is to be expected when writing for an American audience. Another strange thing about the article is how Krugman fails to mention any of the co-benefits that accompany moving beyond fossil fuels: from reduced air and water pollution to lessened geopolitical dependency.

One of the best things about the piece is how is openly recognizes the seriousness of the problem we are addressing:

We’re not talking about a few more hot days in the summer and a bit less snow in the winter; we’re talking about massively disruptive events, like the transformation of the Southwestern United States into a permanent dust bowl over the next few decades.

Too many recent journalistic accounts and government announcements have affirmed the strength of climate science, without elaborating on what that means, and the type and scale of actions that compels.

The piece is probably worth reading for anybody who doesn’t feel like they have a basic understanding of environmental economics, and their relation to climate policy.

Psychological dualism

There is a distinction drawn in theories about the human mind between ‘monist’ and ‘dualist’ understandings of how it works. Dualists, like Descartes, see the mind as essentially separate from the body. Monists believe that “the mind is what the brain does,” and that there is no distinction between the two.

The position of the two views in society is an odd one, as an excellent Paul Bloom lecture discusses. We can readily understand situations that presume dualism: the continued life of the soul after death, the idea that the mind of one person could be transferred into another person or animal, etc.

Hundreds of years before the birth of Christ, Homer described the fate of the companions of Odysseus who were transformed by a witch into pigs. Actually, that’s not quite right. She didn’t turn them into pigs. She did something worse. She stuck them in the bodies of pigs. They had the head and voice and bristles and body of swine but their minds remained unchanged as before, so they were penned there weeping. And we are invited to imagine the fate of again finding ourselves in the bodies of other creatures and, if you can imagine this, this is because you are imagining what you are as separate from the body that you reside in.

Clearly, we are able to imagine minds that would remain essentially unchanged, even when altered into a radically different physical form.

At the same time at dualism seems to make intuitive sense to people, all the physical evidence we have is on the side of a monist view, in which ‘mind’ arises from the physical properties of body:

Somebody who hold a–held a dualist view that said that what we do and what we decide and what we think and what we want are all have nothing to do with the physical world, would be embarrassed by the fact that the brain seems to correspond in intricate and elaborate ways to our mental life.

…

Somebody with a severe and profound loss of mental faculties–the deficit will be shown correspondingly in her brain. Studies using imaging techniques like CAT scans, PET, and fMRI, illustrate that different parts of the brain are active during different parts of mental life. For instance, the difference between seeing words, hearing words, reading words and generating words can correspond to different aspects of what part of your brain is active. To some extent, if we put you in an fMRI scanner and observed what you’re doing in real time, by looking at the activity patterns in your brain we can tell whether you are thinking about music or thinking about sex. To some extent we can tell whether you’re solving a moral dilemma versus something else. And this is no surprise if what we are is the workings of our physical brains, but it is extremely difficult to explain if one is a dualist.

The lecture includes many other examples showing why monism and the world as we observe it seem to mesh.

To me, the importance of this seems to go beyond settling scientific and/or metaphysical questions. It certainly seems plausible that beings that intuitively perceive themselves as essentially independent from physical reality will develop high-level theories about the world that take that into account, in areas as diverse as their religious, political, and moral views. By the same token, if one view really is far more defensible than the other, on the basis of observations and experiments we perform, that quite possibly has moral and political implications. It is all quite interesting, in any case, and I recommend that people consider watching the lecture series. The videos, transcripts, and slides are all available for free online.

Hybrid freezers

The arrival of spring in Ottawa is generally accompanied, for at least a span of time, by violent shifts in temperature. It may be over 10˚C one day, then -10˚C a couple of days later. This is one reason why Ottawa has such broken-up roads and such a constant task of road reconstruction – water gets into cracks on warm days, then freezes and forces them open wider.

One thing this time of year demonstrates is the relatively high certainty that temperatures will stay below freezing for a good span of the year – a situation shared with many other settlements around the world. That reality makes me wonder about the wisdom of having a freezer in my poorly insulated kitchen, using electricity to run compressors and keep the things inside frozen. It seems like it should be fairly practical in places like this to have an outlet to the outside air, similar to those used by driers. The outlet would have a couple of well-insulated doors, one at the entrance to the freezer and one on the outside wall. When temperatures outside were below 0˚C, the freezer would open the doors (when necessary) to keep the contents at the desired temperature. During the summer months, the duct could be disconnected, and a couple of even more well-insulated caps could be put in the freezer wall and outer wall.

A slightly fancier system would not just allow outside air directly into the freezer, but would have sealed loops for outside and inside air that only allow temperature to be passed from one to the other (as with a heat exchanger). That would avoid potential problems with introducing excessive moisture, pollution, etc. Also, and risk of small animals getting inside.

Such an approach would not only be useful for people in my situation. First Nations groups in the Arctic have long relied upon freezing cold winters to preserve meat. Rising uncertainty about whether such frozen caches will actually remain frozen throughout the winter threatens to spoil food. Surely, in such situations, it would make more sense to build insulated shelters that usually rely upon ambient cold to keep food from spoiling, employing an electrical cooling system only when outside temperatures required it.

One little bone and the power of science

A story I read recently about a new species of hominid discovered in Siberia left me feeling struck with the power of science. Inside a cave in the Altai Mountains, a single bone was discovered – the tip of an animal’s little finger. From this, scientists extracted 30 milligrams of mitochondrial DNA. From that, they were able to determine that the creature is an evolutionary relative of modern humans and that, furthermore, it represents a fourth independent instance in which human ancestors radiated out from Africa:

The common ancestor is, however, too recent for the new species to be a remnant of the first human excursion from Africa, the one that led to Java man and Peking man, now known as Homo erectus. It is, in other words, a fourth example of anthropological tourism from Africa to the rest of the world, on what is now looking like a well-worn route. Yet it is the lone example. That shows how fragmentary and ill-understood human history is.

The finger bone was found in strata dated to between 48,000 and 30,000 years ago (the bone itself has not yet been dated). That means the creature was contemporary with both Neanderthals and modern humans in the area.

It seems to me that there has been no other area of human endeavour which could have revealed so much using so little. Certainly, it demonstrates how much information is contained in ancient genetic material, and how powerful its analysis can be for understanding the history of life on Earth.