Anecdotal Evidence and Inductive Conclusions in Psychiatry: Part I

“Can a valid diagnosis be arrived at if laboratory tests are not available? Of course it can. Total reliance on on lab tests to the exclusion of other factors when seeking validity is not science but scientism” ~ Hannah Decker, Ph.D

In my post of April 1, 2010, Is “Data” the Plural of “Anecdote?” I pointed out that in most hard sciences, stories about a scientist or practitioner’s personal experience can be contrasted with “empirical” data from studies, and that the latter usually has more validity that the former.  

As I also pointed out, however, “…many of the randomized, placebo-controlled, double-blind drug studies can be every bit as biased as the worst anecdotal evidence. We are now living in an age of 'marketing-based medicine,' as opposed to evidence–based medicine" (randomized = the use of chance alone to assign the participants in an experiment or trial to different groups; placebo = inert sugar pill; double-blind = neither the person evaluating the research subject nor the subject knows during the experiment if the subject received the placebo or the active medication).

In psychiatry, the situation is even more complex, since there are almost no objective lab tests and we can't read minds, so we must rely on the experimenter's personal observations, or answers by subjects to psychological tests in which we do not know how honest subjects are being or even if they really understand the questions, or patient self reports. All of these sources of data, while important, are highly subjective and can hardly be considered "empirical" in the same sense as, say, a chemical reaction.

Another big point about anecdotes is that they are not worthless in science. Some of the most important discoveries in all of medicine were based initially on anecdotal evidence. In Part II of this post, I will describe how to determine the validity and generalizability of conclusions generated from a group of “anecdotal” clinical observations. That is, how can we tell if the anecdotes are the typical situation seen with a particular combination of clinical variables and which therefore can lead to a conclusion that will probably apply to most patients with a given disorder? Are the conclusions probably true, or probably false? 

In this post, however, I want to contrast conclusions based on a “clinical anecdote” with inductive reasoning. Remember, the first step in the scientific method is observation.

According to Wikipedia, inductive reasoning (as opposed to deductive reasoning) is reasoning in which the premises seek to supply strong evidence for, but not absolute proof of, the truth of the conclusion. It is usually based on seeing the same phenomena over and over again without any exceptions.

The truth of an inductive argument is supposed to be probable, based upon the evidence given. The same phenomena involving two variables are observed repeatedly, and other variables which correlate with the phenomena are shown to be not necessarily connected it, and a tentative conclusion or assumption is drawn regarding the relationship between the two variables.

Deductive reasoning, whose conclusions are more certain, is the process of reasoning from one or more general statements (premises) to reach a logically certain conclusion. Deductive reasoning links premises with conclusions. If all premises are true, if the terms are clear, and if the rules of deductive logic are followed, then the conclusion reached is necessarily true.

To anyone familiar with formal logic, deductive reasoning takes the form of a syllogism:

All men are mortal

Socrates is a man

Therefore, Socrates in mortal

If the first two statements are true, then the third statement must be true. Deductive reasoning is considered the entire basis of science by some scientifically illiterate individuals. 

The problem is that both premises in the above examples are inductive conclusions! Just because all observed men have turned out to be mortal does not in any way prove that the next man you come across cannot be immortal!

The first thing you should have learned from your Geometry 1 class in high school is that there is absolutely no way to prove that the shortest distance between two points on a flat two-dimensional surface is a straight line. It is just that every time you measure it, it is. You just have to assume it.

I have a pen in my hand which I am holding about three feet off the ground. Every time I have dropped it under controlled conditions, it fell to the ground. I can never prove that the next time I let it go, it will fall. So let’s see. Well, I’ll be darned. It did it again!

In other words, ALL scientific deductions are based on premises which are unprovable inductive conclusions. Therefore, presto change-o, if no inductive conclusions are scientific, then no deductive conclusions are either. Or in other words, science would not really exist.

Syllogistically:

              All scientific conclusions are based on inductive reasoning

              Inductive reasoning never proves anything

      Therefore, no scientific conclusions are proven.

Bullcrap.