What is the psychology behind statistics?

On the psychology of statistics¶

To the surprise of many students, statistics is a fairly significant
part of a psychological education. To the surprise of no-one, statistics
is very rarely the favourite part of one’s psychological education.
After all, if you really loved the idea of doing statistics, you’d
probably be enrolled in a statistics class right now, not a psychology
class. So, not surprisingly, there’s a pretty large proportion of the
student base that isn’t happy about the fact that psychology has so much
statistics in it. In view of this, I thought that the right place to
start might be to answer some of the more common questions that people
have about stats.

A big part of this issue at hand relates to the very idea of statistics.
What is it? What’s it there for? And why are scientists so bloody
obsessed with it? These are all good questions, when you think about it.
So let’s start with the last one. As a group, scientists seem to be
bizarrely fixated on running statistical tests on everything. In fact,
we use statistics so often that we sometimes forget to explain to people
why we do. It’s a kind of article of faith among scientists – and
especially social scientists – that your findings can’t be trusted until
you’ve done some stats. Undergraduate students might be forgiven for
thinking that we’re all completely mad, because no-one takes the time to
answer one very simple question:

Why do you do statistics? Why don’t scientists just use common
sense?

It’s a naive question in some ways, but most good questions are. There’s
a lot of good answers to it,[1] but for my money, the best answer is a
really simple one: we don’t trust ourselves enough. We worry that we’re
human, and susceptible to all of the biases, temptations and frailties
that humans suffer from. Much of statistics is basically a safeguard.
Using “common sense” to evaluate evidence means trusting gut instincts,
relying on verbal arguments and on using the raw power of human reason
to come up with the right answer. Most scientists don’t think this
approach is likely to work.

In fact, come to think of it, this sounds a lot like a psychological
question to me, and since I do work in a psychology department, it seems
like a good idea to dig a little deeper here. Is it really plausible to
think that this “common sense” approach is very trustworthy? Verbal
arguments have to be constructed in language, and all languages have
biases – some things are harder to say than others, and not necessarily
because they’re false (e.g., quantum electrodynamics is a good theory,
but hard to explain in words). The instincts of our “gut” aren’t
designed to solve scientific problems, they’re designed to handle day to
day inferences – and given that biological evolution is slower than
cultural change, we should say that they’re designed to solve the day to
day problems for a different world than the one we live in. Most
fundamentally, reasoning sensibly requires people to engage in
“induction”, making wise guesses and going beyond the immediate evidence
of the senses to make generalisations about the world. If you think that
you can do that without being influenced by various distractors, well, I
have a bridge in London I’d like to sell you. Heck, as the next section
shows, we can’t even solve “deductive” problems (ones where no guessing
is required) without being influenced by our pre-existing biases.