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Causal questions

TL;DR

Not every causal-looking question is a valid causal question.

Consider these:

  1. Do vaccines kill?
  2. What is the effect of Vaccine X (versus placebo) on infection rates in a randomized trial?
  3. In smokers over 60, what is the effect of quitting smoking (versus continuing) on 5-year lung cancer risk, adjusting for age and baseline health?
  4. What is the effect of race on income?
  5. What is the effect of parental income on child's future income?

Question 1. and question 4. are not valid causal questions. In 1.

TL;DR

For a causal question to be valid, we need: consistency,