# The Truth (and Lies) of Correlation vs. Causation

Everyday Einstein: Quick and Dirty Tips for Making Sense of Science

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A few weeks ago, our family took a ferry across the English Channel. On the way from England to France, the ferry was extremely crowded, and the crossing took about 75 minutes. On the way back from France to England, there was hardly anyone on the ferry, and the captain announced that the crossing would take 95 minutes.

My 5-year old, wondering why the crossing was going to take longer on the way back, came up with this hypothesis:

“Maybe when there are less people, the boat goes slow; but when there are more people the boat goes faster.”

All the facts seemed to support her, and while this could be possible, I’ll hope you’ll agree that it wasn’t the most likely explanation. My 5-year-old had fallen prey to a classic statistical fallacy: correlation is not causation.

This phrase is so well known, that even people who don’t know anything about statistics often know this to be true. But the thing is, sometimes in science correlation is all you’ve got.

Chopping Latin
The official name for this type of logical fallacy is “Cum hoc ergo propter hoc,” or “with this, therefore because of this.” According to my daughter’s reasoning, after fewer people got on the ferry, the trip took longer. Therefore the trip took longer because fewer people got on the ferry.

It’s easy to see the problem with that logic in these examples:

• “After I washed my car, it rained. Therefore washing my car causes rain.”

• “When I got in the bath tub, the phone rang. Therefore getting in the bath will lead to the phone ringing.”

• “We won our baseball game when I was wearing these socks, so it must be the lucky socks that caused our win.”

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1. 1. jtdwyer 09:09 AM 10/28/13

"But the thing is, sometimes in science correlation is all you've got."

The thing is, if that's all you've got you can't definitively establish causation!

2. 2. curmudgeon in reply to jtdwyer 10:16 AM 10/28/13

"The thing is, if that's all you've got you can't definitively establish causation!"

Never stopped anybody publishing though!

3. 3. drafter 10:39 AM 10/28/13

Jtdwyer & curmudgeon

"The thing is, if that's all you've got you can't definitively establish causation!"
If thats all you have then at least you have a starting point to prove or dissprove. The sad thing is many forget that it is only a starting point and not the end point

4. 4. vapur 05:28 PM 10/28/13

Just like marijuana with a coincidence of schizophrenia.
Just like cell phones contribute to accidents.
Just like GMO promotes the growth of cancer.
Just like video games cause violence.
Just like HIV leads to AIDS.

It is very controversial to go against the popular belief of scientific minds, to question their results and to study anomalies. Being able to establish causation first needs to observe correlations.

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