# Lecture 17 Causal Diagram Practice

## Nick Huntington-Klein

### March 3, 2019

## 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?