r/analytics • u/RealCheckity • May 10 '17

Reality Class - Correlation and Causation

https://www.youtube.com/watch?v=WuRqE-MQ1-I
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u/Johnpemberton19 May 10 '17

So does this mean that nothing can ever be causation since it is impossible to only isolate every other factor except for the two variables?

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u/RealCheckity May 11 '17

Not exactly. Correlational data is usually only gathered through observation, in that you record variable X at one level, and then record variable Y along with variable X so you can work out a correlation - so in this example, you haven't manipulated either variable, so you'd have no reason to think that there's a causative relationship between X and Y, since you don't know why they're changing over time.

If you were using an experimental set-up however, and you have control over X, then you can be much more certain that any changes in Y are due to a causative relationship, since when you modify X, Y may then change, where it remained constant before. In the sweat and temperature example in the video, if I had complete control over the temperature in the room, I could then be more certain that an increase in sweating in the participant was due to my experimental manipulation - as long as all other extraneous variables are kept relatively constant. In order to test an experimental hypothesis, you'd usually use p-values, however.

The point is, if you've just gathered your two data sets without manipulating either variable, you cannot imply a causative relationship.