Statistics: helping you solve life’s more difficult problems…
You might have read recently – since it was in every news outlet here, here, here, here, here, here, and here for example – that recent research has shown that staring at seagulls inhibits them from stealing your food. This article even shows a couple of videos of how the experiment was conducted. The researcher placed a package of food some metres in front of her in the vicinity of a seagull. In one experiment she watched the bird and timed how long it took before it snatched the food. She then repeated the experiment, with the same seagull, but this time facing away from the seagull. Finally, she repeated this exercise with a number of different seagulls in different locations.
At the heart of the study is a statistical analysis, and there are several points about both the analysis itself and the way it was reported that are interesting from a wider statistical perspective:
- The experiment is a good example of a designed paired experiment. Some seagulls are more likely to take food than others regardless of whether they are being looked at or not. The experiment aims to control for this effect by using pairs of results from each seagull: one in which the seagull was stared at, the other where it was not. By using knowledge that the data are in pairs this way, the accuracy of the analysis is improved considerably. This makes it much more likely to identify a possible effect within the noisy data.
- To avoid the possibility that, for example, a seagull is more likely to take food quickly the second time, the order in which the pairs of experiments are applied is randomised for each seagull.
- Other factors are also controlled for in the analysis: the presence of other birds, the distance of the food, the presence of other people and so on.
- The original experiment involved 74 birds, but many were uncooperative and refused the food in one or other of the experiments. In the end the analysis is based on just 19 birds who took food both when being stared at and not. So even though results prove to be significant, it’s worth remembering that the sample on which results were based is very small.
- It used to be very difficult to verify the accuracy of a published statistical analysis. These days it’s almost standard for data and code to be published alongside the manuscript itself. This enables readers to both check the results and carry out their own alternative analyses. For this paper, which you can find in full here, the data and code are available here.
- If you look at the code it’s just a few lines from R. It’s notable that such a sophisticated analysis can be carried out with such simple code.
- At the risk of being pedantic, although most newspapers went with headlines like ‘Staring at seagulls is best way to stop them stealing your chips‘, that’s not really an accurate summary of the research at all. Clearly, a much better way to stop seagulls eating your food is not to eat in the vicinity of seagulls. (Doh!) But even aside from this nit-picking point, the research didn’t show that staring at seagulls stopped them ‘stealing your chips’. It showed that, on average, the seagulls that bother to steal your chips, do so more quickly when you are looking away. In other words, the headline should be:
If you insist on eating chips in the vicinity of seagulls, you’ll lose them quicker if you’re not looking at them
Guess that’s why I’m a statistician and not a journalist.
The issue of designed statistical experiments was something I also discussed in an earlier post. As I mentioned then, it’s an aspect of Statistics that, so far, hasn’t much been exploited in the context of sports modelling, where analyses tend to be based on historically collected data. But in the context of gambling, where different strategies for betting might be compared and contrasted, it’s likely to be a powerful approach. In that case, the issues of controlling for other variables – like the identity of the gambler or the stake size – and randomising to avoid biases will be equally important.
