Archive 2011

Sunday Spinelessness – A rare case of secondary spinelessness David Winter Dec 18

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These Sunday posts are about celebrating the spineless multitude – that under-appreciated majority of animal-life that makes it way around the world without the aid of a backbone. We usualy call thsoe creatures “invertebrates”, but that name doesn’t apply to an actual taxonomic group. These days, taxonomists generally classify organisms based on their shared evolutionary history. So although having a backbone might been the most obvious factor that groups the species in the sub-phylum Vertebrata together, the reason we place fishes, reptiles, amphibians birds and mammals together is the fact they as a group, they are more closely related to each other than any other animals. In fact, the presence of vertebrae in all these groups is one of the reasons we know they are related to each other – since it’s much more likely that the modern species each inherited their backbones from a common ancestor than each coming up with the idea on their own. The ”invertebrates” are simply all the animal species that don’t fall into the group Veterbrata, by they are not a natural group because some of them (like sea-squirts) are much more closely related to vertebrates that other inverts.

Using the evolutionary history of species as a way to classify them leads to some slightly ill-fitting names. The mammalian order Carnivora includes the Panda (an animal that very rarely eats anything other than bamboo) and snakes are still tetrapods even if that name means “four-footed”. As far as I know, there is only one species of vertebrate that lacks a backbone and might therefor sneak in to these posts, the New Zealand endemic Cacaopiscus althaea “or chocolate fish”:

Ok. So the entire post up until this point was a setup for a terrible ‘joke’ (and an excuse to shoehorn some “news” into the Sunday post). For those reading from outside New Zealand, a chocolate fish is a marshmallow (Athaea) filled, chocolate (cacao) covered fish (piscus) shaped confectionery, which has somehow become the standard currency for a small job well done. In that spirit, the doctoral office here at Otago gives everyone that actually makes it to the end of the small task of writing and submitting their PhD thesis a chocolate fish. This is my chocolate fish.

I’d write about my thoughts about the PhD process, the struggles of writing and the inevitable dramas of printing the thing, but I’m not sure my thoughts have caught up with me yet. I’m mainly in the “wandering around the house unsure what to do with myself stage” for now. So if you’ll excuse me, I’ll get back to that.

(repost) Sunday Spinelessness – The origin and extinction of species David Winter Dec 11

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I’m still experiencing a severe spare-time deficiency down here, so, to stop myself from becoming one of those bloggers, here’s something I prepared earlier. 

I chose this post to recycle with good reason, I’m thrilled to say that an edited version of this will appear in print in The Open Lab 2012 - a collection of some of the best online science writing from the last year. Do check out the other entries that made it the anthology, and the other excellent posts that didn’t quite fit into this years collection

I don’t use these pages to write about my own work very much, partly because it’s not yet published and partly because I write about that all day as it is. The shortest answer I can provide to the question “what do you do” is “I use genetic tools to study evolution” and I guess that makes me an evolutionary geneticist. You can split the people that work in our field into two groups: there are biologists that are really interested in a group of organisms and have learned some genetics to help their study of them, and there are people who are interested in a particular question and have chosen their study organisms to suit. I’m very much of the second sort, and like most people in that group I’ve caught myself saying “I’m interested in the questions, not the animals”. Paraphrased, that becomes something like, “Oh sure, I study Pacific land snails, but for all I care they’re just little bags of genes that help me answer questions”. But that’s a lie. You can’t work on animals without having them effect you. When I started my PhD I had no particular love of snails, but now I’m a complete snail fan-boy and I frequently find myself preaching on the wonders of life as a terrestrial mollusc to people whose only mistake was to ask me what I do for a living. Did you know most slugs retain the remnants of their shells? Or that almost all snail shells coil to the right? Or that mating in many land snail species only proceeds after one snail has stabbed the other with a “love dart”? A couple of weeks ago I was recounting the the sad tale of The Society Islands partulids to someone I’d met three minutes earlier, and today I’m going to tell you that story (though, of course you have an advantage over the first recipient of the story, since you don’t have to read this crap)
Believe it or not, land snails are one of the characteristic animals of Pacific Islands. Anak krakatau is so young it’s still smoldering, and it has a native land snail species and Rapa nui (Easter Island), which is arguably the most isolated island in the Pacfic, had its own land snail fauna back when it had forests. It’s not entirely clear how these unlikely colonists get to islands. Darwin was so interested in the question* he, ever the experimentalist, stuck snails to ducks’ feet to see if they’d survive an inter-island journey. Birds have been shown to carry snails great distances, but wind blown leaves are probably a more common mode of conveyance. We might not know exactly how snails get to islands, but we know what happens once they establish themselves. The land snails of the Pacific include some of the most outrageous explosions of diversity in the biological world. Chief among these evolutionary radiations were the partulid snails of The Society Islands (the French Polynesian archipelago that includes Tahiti). Partulids are very elegant tree snails that form part of the land snail fauna across most of Polynesia, in the Societies they made up most of the land snail fauna. In total, the tiny islands had 58 species of these snails with each of the main islands have their own endemic forms.

A plate from Crampton’s monograph on the partulids of Moorea

The Society Islands’ land snails were a marvel all by themselves, but they were also an extraordinary resource for scientists. The first person to seriously take up their study was the American embryologist and evolutionary biologist Henry Crampton. Crampton was working at the turn of the 20th century, a time in which the mechanisms underlying genetics and evolution were very much up for debate, and he hoped Tahitian and Moorean partulids could help set the story straight. Crampton’s monogrpahs are famous (at least among people that spend thier lives thinking about snails) for their detail. He collected and measured over two hundred thousand shells, then calculated summary statistics for each species, each site and each measurement. By hand. To eight decimal places.
Table #95 from Crampton's monograph. Three are approximate 150 cells.
Those massive tables (there are more than 100 pages of them in the Moorean monograph) might seem like an old-fashioned, descriptive, way to do biology. But in many ways Crampton was ahead of his time. For one, he was a Darwinist when not every evolutionist was. By the end of the 19th century Darwin had convinced the world of the fact evolution had happened, but relatively few naturalist bought his theory of how evolutionary change happened. The anti-Darwinian theories that prospered during the so called “eclipse of Darwinism” placed very little importance on the variation within species. The orthogenesists and the lamarckians thought evolution had a driving force, pushing species towards perfection. In their scheme variation within a species was deviance from the mainstream of evolution and was quckly stamped out by natural selection (which they didn’t deny, they just said it couldn’t be a creative force). Similarly, saltationists thought large-scale evolutionary changes occurred in a single generation, and the small changes you see in populations were of no consequence in the grand scheme of evolution. Crampton realised that, in a Darwinian world, variation within populations was the raw material of evolution. He was obsessive about measuring his shells because he knew could use the data he was recording to understand where species came from. In particular, we was able to show that isolated populations of the same species varied from each other. That finding that makes sense in light of Darwin’s theory, since species arise from populations evolving away from each other; but is harder to fit into progressive theories of evolution, in which you’d expect different populations of the same species to follow the same trajectory.
Crampton’s results influenced people like Dobzhanky, Mayr and Huxley who helped to re-establish Darwinism as the principal theory of evolution in the Modern Evolutionary Synthesis. But Crampton also predicted arguably the most important development in evolutionary theory since the modern synthesis. In the middle of the 20th century evolutionary genetics was defined by a single debate. The “classical” school held that populations in the wild would have almost no genetic variation, because for every gene there would be one ‘best’ version and every member of the population would have two copies of that gene. Arguing against the classical school, the “balance” school argued that, quite often, there would be no single best gene and organisms would do better having two different versions of the same gene**. The ballancers thought natural selection would keep lots of different versions of maybe 10% of a species’ genes. Both schools assumed natural selection was such a pervasive force that selection would dictate the way populations were made up, they just disagreed on what would result from it. Here’s the funny thing, they were both spectacularly wrong. When scientists started being able to measure he genetic diversity of populations in the 1960s it became clear almost every single gene had multiple different versions. Now, in the post-genomic age there is a database with 30 million examples of one sort of genetic variant amongst humans.
Faced with the overwhelming variation he recorded in partulid shells, Crampton had argued natural selection didn’t have a damn thing to do with it. Snails isolated from each other by a mountain weren’t adapting to their local habitat, they just varied with respect to traits that had no influence on their survival. The fact two populations were isolated meant each would follow its own path and two populations could drift apart from each other. Faced with the overwhelming genetic variation coming from studies in the 1960s Motoo Kimura proposed the neurtral theory of molecualr evolution. Kimura’s explanation was the same as Crampton’s, almost all of the variation we see at genetic level has no bearing on the success or failure or organisms so the frequency of different variants drifts around at random. The neutral theory is at the heart of a lot of modern evolutionary genetics, and Crampton had understood the underlying principle 50 years before we knew we needed it!
At the end of his monograph on the partulids of Moorea, Crampton said he’d got as far as his measurements could take him, and it was time for someone to study their genetics. In took a bit longer than Crampton might have hoped, but in the 1960s two leading geneticists took up the study of his snails. James Murray from Virginia and Bryan Clarke from Nottingham spent almost 20 years working in what they called, in more than one paper, the perfect “museum and laboratory” in which to study the origin of species. Their work helped scientists understand, among other things, how ecology can contribute the formation of new species and what happens to species when they hybridise with others from time to time. Then, in 1984, Murray and Clarke had to write the most heart-breaking scientific paper I’ve ever read. It’s written in the careful prose scientists use to talk to each other, but the message it delivered was devestating:

In an attempt to control the numbers of the giant African snail, Achatina fulica, which is an agricultural pest, a carnivorous snail, Euglandina rosea; has been introduced into Moorea. It is spreading across the island at the rate of about 1.2 km per year, eliminating the endemic Partula. One species is aiready extinct in the wild ; and extrapolating the rate of spread of Euglandina , it is expected that all the remaining taxa (possibly excepting P. exigua) will be eliminated by 1986-1987.

Euglandina rosea Cga33333
The bad guys: Euglandina on the left, Achatina on the right.

Euglandina rosea is better known as the Rosy Wolf Snail. It senses the mucous trails of other snails, tracks them down and eats them. It’s not clear if the wolf snail had any effect on the pest species it was introduced to control, but it had huge impact on the partulids. By the time Murray and Clarke wrote their paper, E. rosea had already done for one species and it was too well established to control. All they could do was watch as human stupidity and molluscan hunger slowly (1.2 km per year) destroyed the species they’d been studying for 20 years and Crampton had dedicated 50 years of his life to. The same slow torture played itself out in Tahiti and then the rest of the Society Islands. Where there were 58 named species, there are now 5 alive in the wild. Crampton’s hundreds of pages of tables should have been the starting point from which the evolution of the partulids could have been tracked. Murray and Clarke’s natural laboratory should still be open and be taking advantage of a new generation of technologies that might be able to reveal the genetic and genomic changes that occur when a new species arises. Extinction is a natural part of life, and the fate of all species eventually, but when it’s driven by human short-sightedness and robs us of not just a wonderful product of nature but a window through which we might have understood nature’s working it’s very hard to write about.
I should end by saying there is just a tiny scrap of good news in this story. The partulids are no longer an iconic species in the study of evolution, but they have become the pandas of invertebrate conservation. Murray and Clarke were able to get 15 of the species of the islands and into zoos and labs across the Northern Hemisphere. Breeding programs have been succesful, and new lab-based studies come out form time to time. The relict populations back in the Societies don’t have nearly the range they used to, but it appears they’ve held on to most of their original genetic variation. Perhaps, one day, Eulglandina can be taken care of and some of the partulids can have their islands back.

*Darwin had to be interested in dispersal. Before evolution was widely accepted naturalists thought creatures were created for their habitat (the modern creationist notion of a post-flood diaspora explaining the distribution of animals is almost entirely an invention of Seventh Day Adventists, no, really, it is), Darwin’s theory did away with special creation but still needed to explain how life came to live everywhere
** A concept similar to “hybrid vigour”, in which crosses between relatively unrelated strains/cultivar bring together different genes and do well as a result. You’ve seen evidence of this phenomenon any time you’ve eaten yellow and white “honey and pearl” corn. That corn is a hybrid between a white and yellow cultivar and if you count up the kernals you should get close to the 3:1 ratio Mendel preficts for a dihybrid cross.

Some further reading:

Stephen Jay Gould, who was a snail man himself, wrote and essay on Crampton and the Society Island partulids in which made a humanistic argument for the importance conservation. I resisted the urge to re-read it in researching this piece so anything I stole from him I stole sub-consciously!

  • Gould, S.J., 1994. Unenchanted evening in Eight Little Piggies: Reflections in Natural History

Crampton’s monograph on the Mooeran partulids (from which the figures above are taken) is available online

Finally, the paper in which Clarke and Murray told the world about the demise of their snails:

Sunday Spinelessness – Giant weta are amazing… but not the biggest bugs David Winter Dec 04


I’m probably as big a cheerleader as you’ll find for New Zeland’s unique and wonderful invertebrates. So, you’d think I’d be happy to see one of our insects make the pages (or the pixels) of the The Daily Mail, The Sun, Boing Boing, The Huffington Post, The Mirror, The Times of India, io9 and damn near every other blog and newspaper in the world. Instead, I’ve spend the whole time feeling like the grinch that stole the gloss from the headlines.

The story, as it was presented in the tabloids at least, goes that an American tourist traveled to a remote island of the coast of New Zealand where he spent several days searching for a fabled giant bug before finally uncovering the creature and in the process breaking the record for the largest ever insect.

The only problem with the story is that every single detail of it is wrong. The “American tourist” is, in fact, Mark Moffett, former curator of Ants at the Havard Museum of Comparative Zoology turned explorer and a constant feature in National Geographic and in various other media. Little Barrier Island isn’t particularly remote; it’s two hours boat ride from Auckland, almost always has scientific and conservation workers living on it and even has electricity provided by a solar panels. The insect in this photograph is certainly endangered, but it’s apparently not very hard to find on Little Barrier. Most importantly, there is really no way that the insect chomping down on a carrot in this photograph is the largest insect ever recorded. 
The creature in question is a  Giant Weta, wetapunga (“god of ugly things”) in Māori and Deinacrida heteracantha (“mighty locust with differing spines”) in Latin. Here in New Zealand, we give the name “weta” to a large and taxonomically diverse group of cricket-like insects. Most weta are relatively small, not much larger than what you might think of as a standard cricket. Even the small species have a way of freaking people out. Cave weta (called “camel crickets” in other countries that have them) often roost in piles of firewood – I don’t know how many logs have been dropped on how many toes as a result of long antennae an spindly legs poking out form an armful of wood. Perhaps even worse, ground weta (like the hibernating one I recently disturbed) seek cool and dark roosts for the day time, so frequently sleep inside shoes, much to the alarm of  those owners who blindly poke their toes into them and meet resistance.

People that are scared of the smaller weta probably don’t want to contemplate the eleven species of giant weta that make up the genus Deinacrida. The body of these species is about 10 cm long, and they have antennae and legs to add to that (they don’t as io9 and several other outlets suggested, have a “wingspan”, what, with them being flightless). Although the reporting of Moffett’s “discovery” has made a lot about this being the biggest ever giant weta, it’s been rather short on actual numbers. In fact, the one number that keeps coming up in reports is 71 grams. That’s the current record for the heaviest adult insect, and it belongs to a Little Barrier Island Giant Weta, but there is no way the one in this photo can come close to it. In the wild, once weta have mated they move down from the trees in which they live and deposit their eggs deep into soil via that impressive “spike” they carry on their back-end (which is called an ovipositor). However, if you keep giant weta in captivity, unmated and with no access to soil in which to deposit their eggs, they just accumulate egg after egg after egg. The 71 gram behemoth that holds the current record was a captive female, which was retaining eggs and, so, quite unlike anything that would be crawling around trees on Little Barrier. In the wild females with eggs might be able to maintain a weight close to 40 grams. According to people who know, the female pictured with the carrot here isn’t particularly big for the Little Barrier species, so there is no reason to think she approaches the record holder.

I feel a little unpatriotic about this, but I also have to point out that even that 71 gram beast isn’t the largest insect in the world. Goliath beetles (from the scarab beetle family) and the titan beetle (a long horn beetle) probably both beat the the local contender on this front. The internet is full of claims of adult goliath beetles weighing up to 100 grams, but this appears to be one of those fact-like-objects that are often repeated but have no basis in reality. David M. Williams, who has tried to get to the bottom of the largest insect problem, thinks it might be a  result of the the reasonable metric measure “35 grams” entering an imperial brain as “3.5 oz”. In fact, it seems adult goliath beetles probably weight in the order of 30-50 grams – quite likely more than the natural range for giant weta. The titan beetle is longer than the goliath, but it’s not clear that these beetles are bulky enough to weigh more than the giant scarabs. What is clear however, is that the larvae of goliath beetles leave weta in the shade. These 13 cm long grubs tip the scales at around 80-100 grams. Scientists have yet to find the larvae of titan beetles, but they may well get even bigger. I struggle to see a good reason to restrict the “largest insect” to only adult forms, so I’m afraid the weta will have to lose that crown.

I really do feel awful about being such a downer on this rare occasion of a New Zealand invertebrate getting some exposure in the worlds’s press. I trust the poor reporting that came out of the story can be blamed on the tabloids that broke it and the other sources which ran it without doing any checks, and that it’s not a case of someone trying to buy themselves a headline by flying into the country and spotting an insect they knew they’d find. Still, it’s shame that the stories have been about the bogus “discovery” of this animal, and the claim that it’s a record breaker, because there are plenty of good reasons to talk about giant weta. In many ways, these bugs are a prefect example of the wierdness of biology in New Zealand. Our islands are just isolated enough from the rest of the world that, for the most part, invasions from overseas are rare and the bulk of species that live here live nowhere else. Those species that do establish themselves need to adapt to unique conditions and interactions that come with life on our islands, and the results are often very strange indeed. Where else would you end up with the kakapo, a giant flightless parrot in which the males attract mates with a near sub-sonic “boom” that is broadcast up to 5 kilometers from its origin. Giant weta might not be quite as bizarre as the kakapo, but they are a huge flightless cricket that has adapted to life entirely in the trees – that’s pretty cool.

The giant weta exemplify another story that is too common in the New Zealand flora and fauna. The weta and the kakapo seem to have developed in a country that was free from large mammalian predators*, and so never needed to evolve ways to escape or fight off such threats. The introduction of mice, rats, stoats, weasels and possums to our naive ecosystems, and the massive habitat losses that came at the same time, have had a  disastrous effect on our natural heritage. At least 60 species of vertebrate have become extinct since human settlement, and many more invertebrates will have past unnoticed. There are about 150 kakpo left, and only a few mainland enclaves and offshore islands play host to giant weta. Most of the other weta species are doing better than the giants, but they are still having to deal with predators for which their evolutionary history provides them no counter-measures. It’s easy to look at the  recent history of life in New Zealand and feel forlorn - I wish I had the chance to see a pair of Huia feeding or find a half-metre long gecko – but with the weta at least we have a chance to help. The giants need to be managed, and that means we need to make sure the Department of Conservation is funded to the extend that it can live up to its name. The main threat to the smaller weta species, at least in suburban settings, are mice and rats. Providing weta with a few roosting sites that are too slim for a mammal to squeeze into in your garden is enough to stack the odds in the insects’ favour. The Department of Conservation even has plans that you can use to bulid your own weta motel. And for those that think wetas are just too creepy to help in this way – I’m sure providing them safe lodgings will keep them out of your shoes!

You should check Mike Bok’s great post on the biggest insects here and David Williams chapter on the same, discussed above. I’m not going to link to all the news sources that ran with the silly version of this story, by kudos to Alan Boyle at MSNBC and The New Zealand Herald for digging a bit deeper.

 *There are two endemic species of bat, one of which is adatpted to feeding on the ground but probably wouldn’t take on an adult giant weta. There is also a 20 million year old fossil species of mammal that was probably more distantly related to modern placental mammals than marsupials are. We know precisely nothing about how this mammal, or its relatives made a living in New Zealand but the one that got fossilised was very small.

Kiwis blogging about evolution David Winter Nov 29


As any regular readers here may have noticed, my plate is pretty full at the moment. All you are likely to read here for the next little while are quick photo-centric posts about bugs and maybe a few results of my recreational statistics (I know, it’s an illness really) on the New Zealand election.

So, if you are looking for some meatier posts about evolutionary biology and the like, you might want to know that there are a couple of other New Zealanders out there writing on these topics.

Paul McBride is a PhD student from AUT who blogs at Still Monkeys. Paul works on understanding how the ecological setting of a group’s evolution can effect the patterns and rates of change observed in that group. So far, his evolutionary blogging has mostly been about junk DNA and the ways in which we know many of the sequences in genomes serve no particular purpose.

I particularly liked finding out that Susumu Ohno had provided a theoretical argument as to why most of our genome would prove to be useless way back in the 1970s -just as the first genetic sequences were being read in labs. You can add Ohno’s insight to Haldane’s estimate of the human mutation rate (before we knew what a gene was made of!) and Nei’s use of the theory of segregation load to show that most observed genetic changes must occur without the help of natural selection and start to see the wisdom of the elders of population genetics! (Paul also blogs about beer, which suits me, and reminds me to add a post about the science of brewing to my todo list).

Jarrod Cusens is a Masters student, also at AUT, and he blogs at of trees birds and other things. I gather Jarrod’s research is at the hub of evolution and ecology - specifically looking at how to some habitats end up playing host to diverse, species-rich assemblages of organisms while others are dominated by a few species.

Jarrod’s recent posts include a look at a couple of schools in New Zealand who have given up the (very good) biology curriculum in favour of biblical creationism (including one, I’m said to say, in my turangawaewae), a profile of one of the birds that make the New Zealand spring, the shinning cuckoo, with a bit more of the cuckoo’s special brand of parasitism and a whole bunch of quotes.

So, be sure to add Paul and Jarrod to your favourite feed reader, and if you know of any other kiwis bogging about evolution and ecology let met know in the comments.

How did the pollsters go? David Winter Nov 28

A couple of weeks ago I wrote a post comparing the various polling companies that work in New Zealand, trying to see if there were any systematic biases in the results each company produces. In that post, it wasn’t possible to compare each company’s estimates to an external standard because, without an election its impossible to know exactly what the population is thinking. On Saturday night we got to know just what the electorate was thinking, and there were a couple of surprises. 
So, here’s the last estimate of each polling company compared with the results from Saturday night for each of the four parties that made the 5% cut:

The solid line is the election result for each party. Dashed lines are a 95% margin of error for a poll with 1 000 respondents and the given level of support

As you can see, the polls had National too high and New Zealand First too low more or less across the board. It’s hard to say any company did better than the others, Roy Morgan got New Zealand First about right and were the closest to National’s final result, but they made up for that by over-estimating the Green Party and under-estimating Labour.

So, why did most of the companies get New Zealand First and National wrong? Of course, it’s possible that the polling companies had it right, and that people across the nation changed their minds once they had the orange felt-tip pen in their hands. It could also have something to do with who bothered to turn up on Saturday. In the run up to the election, polling companies generally reported around 15% of the electorate were undecided but about 25% didn’t vote. So, some of the people who recorded a preference in a poll didn’t bother to have that preference recorded in the election. As far as I know, New Zealand polling companies don’t ask any questions to determine how likely a respondent is to vote, and ignoring this information could bias their results.

It’s not possible to reconstruct the motivations of those people that didn’t show up on Saturday, but we can look at some data at a coarser grain. If people that express a preference for New Zealand First were more likely to vote than the electorate at large (and so, not including a ‘likely voter’ question in polling would lower their estimate in a poll) then you might expect electorates that really pulled for that party to have higher turnout. It’s not perfect, but it’s all we’ve got, and it doesn’t really fit the story. National actually had stronger support in electorates with high turnout and there isn’t much going on with New Zealand First (I estimate about a 0.8% increase in support votes per 1 000 voters, but that’s not near to significantly different from no increase):

Percentage turnout is calculated relative to total enrollment for electorate (special votes not yet included)

By the way, that graph, with such poor turnout in the electorates that with the largest proportion of Labour voters, might be depressing viewing for Labour supporters. Indeed, I’m sure they’ll want to work on “getting out the vote” in the Māori electorates and South Auckland, but that pattern doesn’t explain the erosion of Labour’s support in this election. Turnout was low in these electorates in 2008. Here’s the support for each party plotted against change in turnout for each electorate (not including special votes):

Sunday Spinelessness – How long ’till they rise up and kill us all? David Winter Nov 27

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The title contains everything i have to say on this video:


Will early returns accurately predict tonight’s outcome? David Winter Nov 26


It’s election day.

I’m sure that later this evening we’ll be treated to one of the staples of election night coverage, results from early returns delivered with the qualifier that they are unlikely to represent a reliable estimate of the final result.

Part of that reason for that qualifier is the obvious point that any small sample only provides an uncertain estimate what’s going on in the population large. That sampling error can be compounded if there is some bias that makes the early-returning booths pull further left or right than the population at large. In New Zealand at least, you’ll often here people say the small polling booths that quickly count and report their results are predominantly from rural areas and, so, favor right wing parties compared with larger, urban booths. (The meme that passes among some right-wing folks, that Labour only won the 2005 election because of  South Auckland voters is an example of this narrative).

So, I thought I’d see if there was any evidence for that these stories are right. It’s easy to get the data from each of the 6 000 or so polling booths used in the 2008 election and munge it together to see if there is a relationship between how red or blue a booth was and how many people voted there (which is a pretty good proxy for how quickly the results will be reported):

If polling booths were unbiased samples of the electorate (they really aren’t…), we’d expect all 99% of the dots in these graphs to fall between those dashed lines.

As you can see, at least in 2008, the common wisdom appears to be wrong: the larger polling booths went more toward National and less toward Labour than the rest of the country.
Tonight’s early results will certainly only be an indicator of where things will end up, but things won’t necessary get better for left-leaning parties as the night goes on.

UPDATE Thanks for a comment from Luis Apiolaza, who suggests a better way of getting the question. These plots show the percent favouring each major party after each polling booth’s data is added in order of how many votes were recorded. As you can see, it takes a long time for Natinoal’s vote to approach its final number. I wonder if this is in part be an artifact of many small booths in Maori electorates? Of course, polling booths won’t necessarily report in order of how many votes were cast in them.

Sunday Spinelessness – Hover fly David Winter Nov 20

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One of these days I’ll use these posts to say something substantive and intersting about the nature of life on earth. Today is not that day. Instead, an old photo of the most common pollinators in New Zealand gardens: Melangyna novaezelandiae, the New Zealand Hover Fly:

Sunday Spinelessness – The 95% David Winter Nov 13

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No the least bit original (1,2), but fun, and entirely featuring critters that have appeared here in the last year or so:

Fans of the spineless may want to join the
Octopi wall street movement of Facebook.

Polling bias among local pollsters? David Winter Nov 09


Lew from Kiwipolitco stumbled across an interesting analysis of Australian pollsters, looking at whether the methods employed by particular polling companies might lead to biases in the numbers they produce .

As that post notes, it’s impossible to tell whether any particular pollster is showing a bias with respect to the real levels of support for each party, because we only find out what the whole population is thinking when we have an election. We can, however, see if a particular polling company is pulling in a different direction than others. Since I’ve had about all the thesis-editing I can stand for one day, I decided to see if the data I put together for those charts from this morning could tell us anything about polling bias among New Zealand pollsters.

 Obviously, the first step is decide on how to find the “average” number against which all polls should be compared. I went with a local regression which just fits a smoothed line through all the points. From there you can measure how far a single estimate is from the smoothed value at the same date*:

Even if all the companies are perfectly sampling the population, we’d expect estimates from single polls to show a good deal of scatter, just because polls are estimates of the population value and come with uncertainty. Indeed, there are dots all over the place in that graph. By collating all those differences between a point and the smoothed lines for the same date we can see if any of the companies are consistently finding higher or lower estimates of a party’s support:

And the answer is… sort of. It seems TV3 tends to get National a little higher and Labour a little lower than the rest of the pollsters, and perhaps the Herald goes the other way. I think trying to gain anything more meaningful than that from these results is probably the statistical equivalent of reading tea leaves, but feel free to stare at the graph and confirm your own political biases!

*You should note, this approach introduces biases of its own and you should take these results with several grains of salt. In particular Roy Morgan polls a lot more often than the other companies, so that company’s polling will contribute more towards the smoothed line than others, so it’s no surprise they show only small biases.

If you are interested in trends in polling bias, I have these differences plotted over time here. As always, I have the raw data here so let me know if you want a csv file to play with.

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