Will One Joint Really Make you Schizoid

1
Will One Joint Really Make you Schizoid?

• Bad Stats Presentation Example

2
Summary

• The original articles from AP, Bloomberg,
  Washington Post, Reuters, and CBS/WebMD said
  that one use of marijuana increases the risk of
  schizophrenia by 40.

3
The Bad Statistics

• The articles implied that marijuana use causes
  schizophrenia. It does not mention the
  possibility of another factor until later in the
  article.
• Implying that a 40 incidence rate is something
  to be concerned about.
• It was not compared with other drugs that might
  be related to an increase in psychosis.
• Alternative views are not presented.

4
What was wrong with them . . .

• Correlation does not imply causation. If the
  stat were completely true, the incidence of
  schizophrenia should go up as marijuana use has
  gone up in the past 50 years, but it has not.
• People who study diseases (epidemiologists) do
  not worry about risk factors until they are cause
  at least a 200 increase.
• Alcohol that leads to an 800 increase in
  psychosis which is much more significant.
• The view of Leslie Iversen, an expert, says there
  is no evidence that marijuana causes psychosis.

5
How should the information have been presented?

• The articles should have stated the facts in an
  unbiased manner. They could write that there is
  a correlation between marijuana use and
  schizophrenia without implying causation. They
  should also mention that schizophrenia rates have
  not increased with marijuana rates. Finally,
  they should have compared their findings with
  other studies. They could have also cited
  different points of view.

6
Note

• Heavy Marijuana users had a 200 to 300
  increased risk. Once again, there has been no
  causation proved.
• Uncovering this faulty reporting of the data is
  not a reason to use marijuana.
• (This is an extra slide.)