DAGs: instrumental and adjusted variables

Question

While drawing DAGs, we can define variables as exposure, outcome and unobserved etc. Could you please explain, what are instrumental and adjusted variables?

Answer 1

While drawing DAGs...what are instrumental and adjusted variables?

An instrumental variable is an observed variable that is often used to help obtain an unbiased estimate for a causal effect that is confounded by another variable that is usually unobserved. The classical situation can be depicted in the following DAG:

Here, X is our main exposure, and the causal effect of X on Y is confounded by U. Z is an instrumental variable for X: it is associated with X (and unconfounded) but not with Y; affects Y only via X; and both Z and Y have no common causes.

An adjusted variable is simply an observed variable which is adjusted for (ie. included as a covariate) in a regression model.