# Lecture 17 Causal Diagram Practice

## Recap

• To make a diagram:
• List all the relevant variables
• Combine identical variables, eliminate unimportant ones
• Draw arrows to indicate what you think causes what
• (See if the model implies that any relationships SHOULDN’T exist and test that)
• Think carefully!

## Recap

• If we’re interested in the effect of `X` on `Y`:
• Write the list of all paths from `X` to `Y`
• Figure out which are front-door paths (going from `X` to `Y`)
• and which are back-door paths (other ways)
• Then figure out what set of variables need to be controlled/adjusted for to close those back doors

## Testing Relationships

• Just a little more detail on this “testing relationships” thing
• Our use of front-door and back-door paths means that we can look at any two variables in our diagram and say “hmm, if I control for A, B, and C, then that closes all front and back door paths between D and E”
• So, if we control for A, B, and C, then D and E should be unrelated!
• If `cor(D,E)` controlling for A, B, C is big, our diagram is probably wrong!

## Testing Relationships

• What are some relationships we can test?