On the Survival of Rats in the Slush Pile | Page 6

constitute a phenomenon which will often be
mentioned in this essay: survivorship bias. We human beings are
fallible creatures, and we have a habit of seeing only the survivors of a
set of experiences. This, Taleb tells us, is an error in thinking which can
get us into serious trouble.
In the course of his draft chapter from the book on black swans, Taleb
sets out to describe several other kinds of erroneous thinking. In order
to illustrate these errors, he asks us to imagine an experiment with rats.
(And since this is a hypothetical experiment I can give an absolute
assurance that no animals were harmed during the writing of this
essay.)

Suppose, Taleb says, that we have access to a city full of rats: rats of all
kinds, fat, thin, sickly, strong, well proportioned, et cetera. In order to
determine which of these rats are the strongest, we select a random
sample, one that is truly representative of the rat population as a whole.
We then put the sample group into a large vat and subject the rats to
increasingly high levels of radiation.
As the levels of radiation increase, many of the rats will die. By the end
of the experiment (unless you take it too far and kill them all) you will
be left with a small number of survivors.
Taleb uses this hypothetical experiment, and its results, to illustrate a
number of errors in thinking.
Flaws in the methodology
First, we need to think about the experimental procedure itself. Alert
readers will already have noticed that the methodology of the
experiment, as described for the purposes of this essay, is flawed.
The intention is to select the 'strongest' rats. But while the experiment
will certainly reduce the numbers of rats, there is no guarantee that the
survivors will be the strongest.
The surviving rats would only be the 'strongest' in the limited sense that
they were the ones best able to withstand increasing doses of radiation.
They might not be the strongest in terms of ability to survive without
water, or ability to climb fences. The ability to withstand radiation
might or might not be a useful characteristic in the real world.
Second, at least some of the survivor rats may have survived by pure
chance. At the moment when the next blast of radiation was
administered, a 'weak' rat may have been shielded from radiation by a
'strong' rat. Furthermore, there might be some variations in the way in
which the radiation was distributed around the vat: in some spots
(perhaps towards the rim) the rats might absorb less than in other spots.
In short, the design of the procedure leaves much to be desired; and this,

we shall see, is the case with some procedures in publishing.
Survivorship bias
We have already noted the phenomenon which is known in statistics as
survivorship bias; and history suggests that it is all too easy to fall prey
to this lax way of thinking.
Survivorship bias involves mistaking what you see for what is really
there. The tendency is for human beings to see only the survivors of
some set of circumstances, and to ignore those who, for one reason or
another, disappeared or dropped out as events proceeded. We often find
ourselves earnestly discussing the traits in a cohort of survivors when,
in truth, those traits are no different from those in a much larger
population; if you consider the circumstances carefully it may be
apparent that the survivors emerged as a result of sheer randomness,
rather than through the possession of some special qualities.
It may be, if clear thinking is applied to any set of events, that those
who dropped out, voluntarily, or were eliminated, perhaps as a result of
chance, have at least as much to teach us about what is important and
relevant as those who survived.
Nietzsche's error
Nietzsche is responsible for the aphorism 'What does not kill me makes
me stronger.' If repeated, in a suitably solemn tone of voice, in front of
a group of people who are aware that Nietzsche is a Big Name in
Philosophy, this dictum may well induce nods of agreement. And you
may sometimes hear people say, after a young person has had some
kind of setback, 'Well, he will be all the better for the experience.' Once
in a while it might even be true.
In general, however, Nietzsche's aphorism is nonsense. On the physical
level, a car crash which brings you close to the point of death may
leave you paralysed for life. So, although you are not actually dead, you
are certainly not stronger than before. And in an emotional context, a
bereavement which causes you seriously to contemplate suicide may,

even if you do not succumb to the temptation, leave you lonely