Wikipedia mammals and the power law

Playing a bit more with the Wikipedia mammal data, there are some interesting patterns to note. The first is that rank the mammal pages by size (here defined as the number of characters in the source for the page) and plot size against rank then we get a graph that looks very much like a power law:

There are a few large pages on mammals (these are on the left), and lots of small pages (the long tail on the right). If we do a log-log plot we get this:

The straight line is characteristic of a power law. The dip at the far right reflects the fact that Wikipedia pages have a minimum size (for example, they must include a Taxobox). Now, this is a bit crude (I should probably look at "Power-law distributions in empirical data" arXiv:0706.1062v2 before getting too carried away), but power laws are characteristic of the link structure of the web (a few big sites with huge numbers of links, huge numbers of sites with few links), and indeed of at least parts of Wikipedia, such as the Gene Wiki project (see doi:10.1371/journal.pbio.0060175).

In this context, the diagrams are showing that even if mammals are "charismatic megafauna", most of them aren't that charismatic. Wikipedia mammal pages are mostly small. This raises the question of whether the high frequency in which Wikipedia mammal pages appeared in the top of Google searches might be attributed to those large pages on (presumably) charismatic mammals. If this were the case, then we'd expect that small pages wouldn't rank highly in Google searches. So, I plotted page size against Google search rank for the Wikipedia mammal pages:

This is a box plot, where the grey boxes represent 50% of the distribution of page size (the horizontal black line is the median), and extreme values are shown as circles. Note that "0" is the highest rank (i.e., the first hit in Google), and 9 is the lowest.

While, not surprisingly, most large Wikipedia pages do well in Google searches, and rarely are large pages low down the rankings, my sense is that small pages can have any rank, from top (0) to bottom (9). If page size (i.e., which is a crude measure of the effort put into editing a Wikipedia page) is a measure of "charisma" (contributors are more likely to edit pages on animals that lots of people know about), then charisma isn't a great predictor of where you come in Google's search results. It's not about size, it's about being in Wikipedia.

Google, Wikipedia, and EOL

One assumption I've been making so far is that when people search for information on an organism using its scientific name, Wikipedia will dominate the search results (see my earlier post for an example of this assumption). I've decided to quantify this by doing a little experiment. I grabbed the Mammal Species of the World taxonomy and extracted the 5416 species names. I then used Google's AJAX search API to look up each name in Google. For each search I took the top 10 hits and recorded for each hit the site URL and the rank in the search results (i.e., 1-10). Below is a table of how many mammal species had a hit in the top 10 Google results (showing just the top 20 most frequent sites).

Site	Hits
en.wikipedia.org	5266
species.wikimedia.org	2934
animaldiversity.ummz.umich.edu	2890
commons.wikimedia.org	1515
www.itis.gov	1418
ctd.mdibl.org	1288
www.bioone.org	1101
www.uniprot.org	1086
encyclopedia.farlex.com	1007
www.thewebsiteofeverything.com	955
www.answers.com	864
vertebrates.si.edu	854
www.interaktv.com	842
www.arkive.org	775
linkinghub.elsevier.com	727
www.springerlink.com	656
www.eol.org	618
www.reference.com	576
doi.wiley.com	572
noctilio.com	566

Wikipedia is the clear winner, with 5266 (97%) of mammals having a Wikipedia page in the top ten Google results. Next comes Wikispecies, then Animal Diversity Web, Wikimedia Commons, ITIS, the Comparative Toxicogenomics Database, BioOne, UniProt (derived from the NCBI taxonomy), and so on. Note that the Encyclopedia of Life comes in 17th.

Things get more interesting if we look at the ranking of search results. The graph below plots the cumulative rank of search results for some of the web sites listed above.

Wikipedia dominates things. For 48% of all mammal species Wikipedia is the first result returned by Google. Just under three quarters of all mammal species are either the first or second top hit in Google. The next best sites are Animal Diversity Web and Wikispecies, which get a small share of first place for some species (19% and 7% respectively). Note that EOL pages manage to make it into the top 10 for only 11% of all mammal species.

What does this all mean? Well, it seems clear that if people are using Google to find information about an organism, then Wikipedia is more likely than anything else to be the first result they see. It is also interesting that for all the energy (and funds) being expended on biodiversity databases (doi:10.1126/science.324_1632), ITIS is the only classical biodiversity database that routinely gets found in these searches (albeit in only a quarter of the searches).

I know I tend to go on a bit about EOL, but if I was running (or funding) EOL, I'd be worried. EOL barely figures in these search results, and is being taken to the cleaners by a volunteer effort (Wikipedia). Furthermore, it seems difficult to envisage what EOL can do to improve things. Sure it can link to (and make use of) content in sites such as Animal Diversity Web, ITIS (and maybe even, gasp, Wikipedia), but that just adds "link love" to those sites. Ironically, perhaps the single thing that would improve EOL's ranking would be if Wikipedia spread some of its link love over EOL, by linking all it's taxon pages to the corresponding EOL page.

But there are bigger issues at stake. Site popularity on the web tends to follow a power law, where a very few web sites grab the vast majority of eye balls. In a old blog post Clay Shirky wrote:

Now, thanks to a series of breakthroughs in network theory by researchers ... we know that power law distributions tend to arise in social systems where many people express their preferences among many options. We also know that as the number of options rise, the curve becomes more extreme. This is a counter-intuitive finding - most of us would expect a rising number of choices to flatten the curve, but in fact, increasing the size of the system increases the gap between the #1 spot and the median spot.

So, creating new and improved biodiversity web sites is likely to have the effect of only increasing the gap between Wikipedia and the rest.

Lastly, as I've mentioned before regarding Wikipedia and citations of taxonomic work, the graph above suggests to me that for anybody wanting to make basic biodiversity information available on the web, and attract readers to basic taxonomic literature, there really is only one game in town.

Comparing Wikipedia and Mammal Species of the World classifications

Continuing the saga of making sense of the mammal classification in Wikipedia, I've done a quick comparison with the Mammal Species of the World (third edition) classification. MSW is the default taxonomic reference used by WikiProject Mammals. I downloaded the MSW taxonomy as a CSV file (warning, it's big), and wrote a script to pull out the classification as a GML file (my preferred graph format).

Based on some earlier work with Gabriel Valiente, I wrote a simple program that takes two trees and highlights the nodes in common to the two trees. I then input into this program the MSW tree, and the largest component of the graph of Wikipedia mammals. The MSW tree has 13582 nodes, the Wikipedia tree has 6287. Note that Wikipedia has more taxa than these 6287 nodes suggest, but they aren't connected to the largest tree (often due to intermediate nodes in the classification lacking a page in Wikipedia). The two trees have 4935 nodes in common (again, this number will be a little low, there are some weird taxon names due to problems parsing Wikipedia).

MSW versus Wikipedia
Below is a the MSW classification with taxa in Wikipedia shown in red.

[Larger scale view here]

The impression given is that most Wikipedia mammal pages are in MSW, with some notable exceptions, including higher level taxa such as Afrotheria, and extinct taxa such as the Multituberculata. Some extant taxa are missing due to synonymy. For example, Wikipedia gives the scientific name of Anthony's pipistrelle as Pipistrellus anthonyi, whereas MSW has it as Hypsugo anthonyi.

As an aside, Wikipedia pages often get muddled about parentheses around taxonomic author names. The authority is in parentheses if the current genus is not the original genus the species was placed. Hence, Pipistrellus anthonyi (Tate, 1942) should actually be Pipistrellus anthonyi Tate, 1942, as Tate originally described this taxon as a species of Pipistrellus (see hdl:2246/1783). However, the name Hypsugo anthonyi (Tate, 1942) does need parentheses.

Some Wikipedia taxa also postdate the publication of MSW, such as Philander deltae (see doi:10.1644/05-MAMM-A-065R2.1).


Wikipedia versus MSW
When we do the reverse comparison we see something rather different.

[Larger scale view here]

This is the MSW tree, coloured red where the MSW taxon has a page in Wikipedia. There are big gaps, some of which are due to those pages being in another component (in other words, many "missing" taxa do have pages in Wikipedia, they are just not properly linked to the bigger tree). MSW is also rich in subspecies, which tend to lack their own pages in Wikipedia (possibly a good thing in the cases of taxa such as pocket gophers).

It would be nice to make these comparisons automatic, and develop tools so that managing taxonomy in Wikipedia could be made easier.