I would summarize many of my driving interests under the heading of “scientific epistemology”. However, for a long time I had an egregious blind spot: statistics. Although I read my way through Rohlf and Sokal’s classic text “Biometry” six years ago, it left me with something less than a working understanding of statistics as a research scientist would use it. Whether this was my fault or the text’s, or simply a matter of incompatibility, is hard to say.
To ameliorate the situation, I spent much of my spare time last April plowing through each and every chapter of “Discovering Statistics Using R” by Andy Field (and co-authors). On the whole, it was an immensely enjoyable experience. Here are a few of my meta-insights.
- You can grasp the statistical concepts without becoming a mathematician. I sometimes have difficulty assimilating knowledge if I fail to understand its foundations — e.g. to learn how a drug is used without understanding its molecular mode of action. This difficulty persisted even after I had identified it as a hindrance. (This is part of why I wandered from medicine into the history and philosophy of science, where an obsession with foundations is generally a natural advantage.) Analogously, I was worried that I might get stuck with my statistics text as soon as I encountered some mathematical theorem that I had to accept but couldn’t understand with reasonable effort and within reasonable time. Happily, I found it easy to deal with mathematical black boxes in statistics. I think two things helped. First, DSUR introduces the black boxes efficiently and often labels them explicitly, which makes it easier to accept them. Second, many statistical black boxes can be grasped intuitively. For instance, there is the “variance sum law”, which states that the variance of the differences or sums of two independent variables is equal to the sum of the variances of the two variables (this matters, for example, if you are testing whether the means of two populations differ in a t-test). I don’t know how you prove this (although it is not difficult to imagine the outlines of a proof), but I nevertheless find it highly plausible that the variance sum law holds. Other questions are more difficult — e.g., why do correlation coefficients range from -1 to 1? Mathematician friends tell me that the answer to this is nontrivial. Nevertheless, I did not have any difficulty accepting it, and so my education in statistics could proceed. I found that there were many similar instances of very tolerable black boxes.
- Statistics should be seen in relation to concrete study designs. When I read “Biometry”, I think I lost the forest for the trees: I learned about the theory of statistics but failed to see how it applied to concrete research situations. One of the strengths of DSUR is that it is pretty clear about how each statistical method relates to familiar types of study designs.
- The importance of the computer is hard to exaggerate. “Biometry” was originally written in the 1970s, and its primary tool was the pencil: It taught me how to do statistics by hand, if necessary. I get that this can be useful for teaching concepts. But in practice (and in 2014) I found it vastly more enjoyable to study statistics in close contact with R, where I learned how to actually work on more or less realistic data sets. I like to joke that I love computers and will take any excuse to spend more time with them. More seriously, I think that doing statistics is pretty similar to programming: Understanding the concepts is one thing, but you also need to learn which functions take which values, where to put the semicola, and what the error messages mean. There is a craft to statistics, and I think that familiarity with the craft makes it easier to assimilate the theory.
- Emotions matter. It is well know that learning without positive emotion is difficult for us humans. Importantly, therefore, DSUR helped me to get excited about statistical methods. I get that you should have a good conceptual grasp of the assumptions that a data set must meet if you want to do an ANOVA. But studying those assumptions before you have ever done an ANOVA and thus before you have discovered the potential power of the method is, frankly, boring. DSUR helps you to see — more importantly, to feel — that statistical methods are really cool and powerful, and this helps you through more tedious things like checking whether your data are homoscedastic.
- Philosophy of science is useful. During the first half of the book, in the throes of young romance, I felt that statistics is the key to understanding scientific epistemology and in some sense removes the need for a philosophy of science. But I quickly recuperated: I now think with renewed conviction that the philosophy of science is tremendously important. It should be taught alongside statistics to students. One cannot make sense of scientific methodology by understanding only statistics but none of the concepts that traditionally live in the philosophy of science. Statistics texts hardly touch many of these questions: What is a cause? What is the logic of causal inference, and what are its prerequisites? (Which is the basis for asking: And how does statistics help in inferring causes?) What is the epistemological role of scientific models? What are mechanisms, and what does it take to ascertain them? How do causal processes at different levels of organization relate to each other? What is an explanation, and what role does explanatory power play in the confirmation of scientific hypotheses? Many of these questions do not (currently) have definitive answers. But I do think (based on experience) that most working scientists have strong intuitions about them that help them in their epistemological work — and if nothing else, the philosophy of science can prime these intuitions and help to produce better scientists. To my surprise, then, an immersion in statistics has helped me to better appreciate one of my parent disciplines (which are, in this order: biomedicine, history of science, and philosophy of science).
2 thoughts on “What I learned by discovering statistics using R”
Great blog post! – From a personal view, I hold the notion of simplicity in high esteem, especially in statistics where people seem keen to apply the latest and most calculation-intensive methods. Quite often, you can make strong statements without using fancy tests that assume normal distribution of the input variables or the like. I'm thinking non-parametric methods and similar stuff that often even works on quite small sample sets, such as the permutation test, see http://en.wikipedia.org/wiki/Resampling_%28statistics%29#Permutation_tests
I like the simplicity of the non-parametric tests. The author of DSUR claims, however, that the future belongs to the computationally more intensive bootstrapping approaches, which do a lot of the traditional tests with fewer assumptions (so in a way it's the best of both worlds). This sounded right to me, but I'm not qualified to judge.
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