'Real-life' examples of reasoning errors wanted

[Elaedith]

I am giving a lecture next week on human reasoning and reasoning errors (to social science students). I want to cover several topics including (briefly) a couple of examples of formal reasoning errors (post-hoc fallacy, illicit conversion). We would later be discussing possible relationships between reasoning errors and 'magical' thinking, illusory correlations, and other everyday phenomena.

We had already looked briefly last week at formal reasoning of the type (If P then Q, P, therefore Q) and we looked at the fallacy of affirming the consequent. We also demonstrated this with the Wason selection task. The first thing the students want to know is what relevance all this has to 'real life' as they rarely have any exposure to formal argument.

I can think up many examples of the post-hoc fallacy in real life, but I have more trouble with the illicit conversion case.

One example I came up with last year was the following: An organisation sent warnings to members about fake emails sent by account hijackers. The warning stated 'If an email is from us, it will address you by name'. Shortly after, several members received emails addressing them by name and asking for their account details. These people were convinced the letters were genuine, and ended up having their accounts stolen. They subsequently blamed the organisation for telling them that 'if an email addresses you by name, it comes from us'. In other words they had wrongly converted 'if its from us, then it addresses you by name' to 'if it addresses you by name, then its from us'. I believe this qualifies as a real life example of illicit conversion.


I have trouble thinking of examples. Most of the examples of this particular fallacy seem to apply more to formal argument. I would appreciate suggestions for any other examples similar to the one I gave, or any example of unusual 'real life' illustrations of reasoning errors.

[thaiboxerken]

Averts are a wealth of fallacy. You could also look at religion.

[blutoski]

I am giving a lecture next week on human reasoning and reasoning errors (to social science students). I want to cover several topics including (briefly) a couple of examples of formal reasoning errors (post-hoc fallacy, illicit conversion). We would later be discussing possible relationships between reasoning errors and 'magical' thinking, illusory correlations, and other everyday phenomena.

We had already looked briefly last week at formal reasoning of the type (If P then Q, P, therefore Q) and we looked at the fallacy of affirming the consequent. We also demonstrated this with the Wason selection task. The first thing the students want to know is what relevance all this has to 'real life' as they rarely have any exposure to formal argument.

I can think up many examples of the post-hoc fallacy in real life, but I have more trouble with the illicit conversion case.

One example I came up with last year was the following: An organisation sent warnings to members about fake emails sent by account hijackers. The warning stated 'If an email is from us, it will address you by name'. Shortly after, several members received emails addressing them by name and asking for their account details. These people were convinced the letters were genuine, and ended up having their accounts stolen. They subsequently blamed the organisation for telling them that 'if an email addresses you by name, it comes from us'. In other words they had wrongly converted 'if its from us, then it addresses you by name' to 'if it addresses you by name, then its from us'. I believe this qualifies as a real life example of illicit conversion.


I have trouble thinking of examples. Most of the examples of this particular fallacy seem to apply more to formal argument. I would appreciate suggestions for any other examples similar to the one I gave, or any example of unusual 'real life' illustrations of reasoning errors.

I have a logical fallacy tutorial with example exercises (http://www.bcskeptics.info/resources/criticalthinking/practice.html). You can tweak these to reflect local circumstances.

[Jeff Corey]

I am engaged in studying the Wason Card Selection task and feel that its demonstration of confirmation bias has "real life" relevance in a number of areas.
Alternative medicine, superstitions such as the Lunar Lunacy effect, dowsing, and other dubious practices persist because confirmatory data are actively sought out and falsifying evidence is ignored.
This would be particularly harmful in police investigations.

[drkitten]

I am giving a lecture next week on human reasoning and reasoning errors (to social science students). I want to cover several topics including (briefly) a couple of examples of formal reasoning errors (post-hoc fallacy, illicit conversion). We would later be discussing possible relationships between reasoning errors and 'magical' thinking, illusory correlations, and other everyday phenomena.

Kahneman and Tversky, Judgement Under Uncertainty list a plethora of examples of inability
to judge probabilities correctly, even in a comparative sense.

[Jorghnassen]

This is published bad reasoning. (http://news.bbc.co.uk/1/hi/health/1331401.stm) But don't take my word for it. (http://www.canadian-universities.net/News/Press-Releases/September_8_2006_McGill_researchers_debunk_Oscar-winner_longevity_b.html)

[666]

Well, if the "Oscar Winners Live Longer" story of 2001 has been debunked, now we have the "Nobel Prize Winners Live Longer" story of 2007!
http://education.guardian.co.uk/higher/research/story/0,,1992374,00.html

[Kopji]

We had a business leader create an entire department of 20 people in another city (say City "B") in case the mainframe computer in (say city "A") suffered a disaster. The terminals in city "B" connected to.... you guessed it - the mainframe in city "A".

[Jorghnassen]

Well, if the "Oscar Winners Live Longer" story of 2001 has been debunked, now we have the "Nobel Prize Winners Live Longer" story of 2007!
http://education.guardian.co.uk/higher/research/story/0,,1992374,00.html

Let me read it first...

[ChrisC]

Thanks, blutoski. I found your tutorial really useful. Just the kind of intro I've been looking for.

[ICBS]

Well, if the "Oscar Winners Live Longer" story of 2001 has been debunked, now we have the "Nobel Prize Winners Live Longer" story of 2007!


Wow. Big improvement... NOT.

They missed the major reason their study is crap. It never ceases to amaze me that people with so little understanding of research design - heck, logic - continue to get published.

I should have known my first post here would be to call some study "crap". Sorry in advance, but that's what I do most of the time...

ICBS....... Everywhere

[ttias]

Execuse my ignorance, I'm from Sweden. Does illicit conversion mean that you mistake the logical "if...so" relationship for the "if and only if" relationship?

[Big Al]

There is a strong correlation between children's shoe sizes and verbal ability. Therefore, if your child has big feet, he or she is likely to be a good reader.

Errr... there is also a very strong correlation betwen children's shoe sizes and their ages!

Or:

"Doctor, doctor, I keep getting a sharp pain in my right eye when I drink tea! Am I allergic?"

"Try taking the spoon out of the cup when you've stirred it."


Or:

"When I eat a takeaway after a solid weekend of boozing, I feel dreadful on Monday morning. Perhaps I should cut down on Chinese food."

[Elaedith]

Thanks for the suggestions, it turned out that we had plenty to talk about. This class picks things up quickly, when we got on to characteristics of magical thinking they came up with the example of homeopathy by themselves.

Execuse my ignorance, I'm from Sweden. Does illicit conversion mean that you mistake the logical "if...so" relationship for the "if and only if" relationship?


That is how I understand it. When I go over it I try to relate the 'and only if' part to the need for controlled studies.

[ttias]

That is how I understand it. When I go over it I try to relate the 'and only if' part to the need for controlled studies.

Cool. I learned some new English then. Thanx.

[Skeptic Ginger]

Nice collection of examples, blutoski.

I use the following in some of my infectious disease classes.

12 people in an office get flu shots and they all get sick the next day.
Why is this not evidence the flu shots made them ill?

Because there were 12 other people in the same office who also got sick and who did not get flu shots.

A sample is meaningless without controls for other variables.

You got a flu shot 3 years in a row and you became ill within a few days each time.
Why is this not evidence the flu shots made you ill?

Personal experience distorts our perception of the facts. This is a sample size of three with no controls. Would you want a drug that was tested on three people? If you wore your hat backward at the homecoming game three years in a row and your team won each time, would you then believe wearing your hat backward was the reason?

Because we observed it ourselves, it's very hard not to give in to drawing the false conclusion.

When we do observe such things, rather than forming a belief, we should form an hypothesis and TEST it.

Break a window with a hammer and you know the hammer caused the break, how does that differ? Because breaking windows with hammers has been sufficiently established as cause and effect.

We falsely conclude it has been established flu shots make people ill. It is important to begin to recognize conclusions we believe have been established that have not really been established.

In reality, placebo controlled studies have established influenza vaccine almost never produces "flu like symptoms", aches, fever, or any other systemic effect. A small percentage of people get a mild sore arm after flu shots. Young children might feel poorly the day after, it's generally very mild and it didn't happen to adults in the studies.

We give flu shots in Oct-Nov when other respiratory infections are peaking in incidence. It is common to become infected around the same time a flu shot is given. You would expect to have a number of people becoming ill by coincidence at the same time as their flu shot.

[Skeptic Ginger]

I would also bring in some examples of commercial products with misleading if not outright false advertising.

Listerine kills germs that cause bad breath does not mean Listerine stops bad breath. The germ killing effect of Listerine is so minimal it doesn't even meet the FDA standard to be listed as an antiseptic. See for yourself at the FDA's web site.

Same thing with Lysol, another falsely promoted product. It is a low level disinfectant but there is no evidence using it has any impact on any infections in your home. Perhaps in a hospital or daycare Lysol might decrease infections by a very small amount over simple cleaning. In those 2 cases, use an EPA registered disinfectant meeting the standard needed for the surface being cleaned. For example, running plastic toys through the dishwasher is much better than wiping them off with Lysol.

Airborne and Headon make various statements on their labels and in their ads all intended to leave the false impression they are claiming their products actually do something. No where on the labels or ads are there any direct statements the products are effective for the conditions they are sold to prevent or treat. They can't make the claims because there is no evidence either product does anything.