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Just how big is that effect size?

24 Jan

On Monday The Washington Post ran a story with this headline: “Teens who spend less time in front of screens are happier — up to a point, new research shows.”

What the article does not tell us (but the abstract does) is the that the study had 1.1 million participants. Well that seems like a good thing, doesn’t it?

The problem is that with a sample that large almost any correlation will be statistically significant. For example, according the Post account, the correlation between texting and happiness was r = -.05. Typically a correlation of the this magnitude would be described as “none or very weak.” 


Testing a hypothesis: Over 21 edition

24 Apr

Tonight, I am going to lecture about hypothesis testing. I plan to show my students this video I found on BoingBoing:

The question for the students: was this a fair test?

Correlation is not causation (nudge, nudge, wink, wink)

4 Jul

There is no end to the media presenting correlations as causation. I was struck by this piece in Monitor on Psychology a publication of the American Psychological Society. I think I see a pattern here:

  1. Point out some correlation
  2.  Say that the researchers “controlled for other variables” (always a dubious claim)
  3.  Quickly acknowledge that correlation is not causation
  4. Never report the magnitude of the effect
  5. Write the rest of the article as if causation has been established


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