Cork Skeptics

Promoting Reason, Science & Critical Thinking in Cork City & Beyond


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Logical fallacies: Part 1: You can’t believe everything you hear

Being a critical thinker means looking at facts carefully, critically and logically. There is no person or place that can be a repository of all knowledge, no-one knows all the answers or even has all the facts. In light of this we need tools to examine claims, tools that can steer us in the right direction even if we know little about the subject until we can find more information about it. However, there are certain forms of bad arguments, poor reasoning and illogic that are easy to spot, no matter their surroundings.

When you come across a logical fallacy in conversation you should flag it with your skeptical Flag of Examination and examine its claims critically.

I’m going to split this subject up into small digestible pieces over my next few posts.

Recently intrepid members of Cork Skeptics went to the local Mind, Body, Spirit trade fair (more about this if you attend our session on Friday). It was ablaze with colour, and filled with people young and old, most of whom were pleasant, good-natured and keen to chat about their wares and very open to answering skeptical questions. It is easy to see why people are left with the impression that alternative therapies really work when they are assured face to face by earnest, sane, well-spoken adults that it does. We all assume that on the whole people are trying to be honest and truthful when they speak. So how do you spot problems when you know that the person telling you about is not deliberately trying to deceive you?

Probably the most striking thing about all festival for me was that whether the purveyors were selling crystals, readings, colours, scents or physical manipulations, there was one thing they all had in common. They all used anecdotes to convince buyers of the efficacy of their product. These are perhaps the most commonly used logical fallacies of all and are often used in complete innocence by people who sincerely believe that personal stories count as evidence.

Anecdotes are not evidence

Personal stories and testimonies get around. However, they do not constitute proof of anything by themselves.

This comes as a bit of a surprise to a lot of people. After all, even courts take evidence from witnesses. However, as any policeman or lawyer will tell you, eye-witness testimony is horribly unreliable. Even the sincerest witness can get things completely wrong; perhaps by accident, perhaps they were intentionally misled, sometimes simply because they have attached a meaning to an incident that just isn’t there.

The Selective Attention Test here provides an illustration of how people can miss the blindingly obvious once their attention has been directed elsewhere.

In the test in this video, viewers did not notice the gorilla at all because they had been asked to count the number of passes made by people in white shirts. It seems hard to believe, but there you go: the power of human observation (or lack thereof).

Read more about the Invisible Gorilla experiment here.

The best you can claim for a plethora of anecdotes seeming to support an argument is that it might be grounds for genuine investigation of the facts.

 

After-the-fact reasoning

One of the reasons why people so often think that an anecdote is convincing is because they make another common mistake. This involves taking the end result and then trying to backwards engineer a cause.

It is a leap of illogic that doesn’t bother to eliminate other possible causes before announcing that X must have caused, or be proof of Y.

Example:

I won the first two matches and I was wearing my red T-shirt. I lost the third match and I was wearing my white T-shirt. Therefore my red T-shirt must be lucky.

Or:

I went into hospital to have my appendix removed, and I put special healing crystals around my bed. Now I have recovered quickly from my surgery without any complications. Therefore, the crystals must have special healing powers.

In both examples other (more likely) contributing causes are completely discounted in favour of a pet theory.

In the case of alternative medicine the bulk of the favourable evidence offered as “proof” of efficacy tends to fall into these categories. Very often no real scientifically conducted double-blinded tests have yielded anything positive beyond placebo. This is not to say that all alt-med treatments cannot work, just that those with only anecdotes to bolster their claims they have not proved their case at all.

 

Further reading:

Ben Goldacre’s Bad Science

Steven Novella’s Neurologica

Science Based Medicine

Respectful Insolence

 

 

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Acupuncture and fertility

The Irish Independent recently published an article purporting to show that acupuncture can aid pregnancy. To a skeptic, such news items also shows us why anecdote alone is often a bad indicator of extraordinary claims. Anecdote does not guard against the “Post Hoc ergo Propter Hoc” fallacy – the idea that if something was done before an event, then it somehow must have caused that event. This is irrational thinking on a par with rain dancing, throwing salt over your shoulder after spilling it and sacrificing a goat to prevent a volcanic eruption. As any scientist will tell you, determining causation is a tricky business. You need to eliminate other more likely competing causes, systematically reduce the effects of experimenter bias and have a big enough data set to see a universal effect. Failing this kind of experimentation you have two occurrences – the use of acupuncture and the onset of pregnancy – with the only connection being a strongly held belief that one event caused the other.

Brian Hughes over at The Science Bit has written a well argued piece on the Independent article where he looks at the evidence supporting acupuncture and increased fertility. It’s well worth a read.