IDEA FOUND // IDEA 134
Directed Acyclic Graphs
“An arrow diagram forces the causal story into the open before the statistical model is touched.”
01 / PLAINLY
What it means, plainly
A directed acyclic graph, or DAG, draws variables as points and assumed causal links as arrows. ‘Acyclic’ means the directed arrows do not loop back to their starting point.
02 / CONTEXT
A little more
A DAG represents variables as nodes and assumed causal relations as arrows without directed cycles. It supports reasoning about open paths, adjustment, and assumptions that data alone do not establish.
03 / WHY IT MATTERS
Why it matters
It makes the assumptions behind comparisons and adjustments visible so they can be debated before the analysis begins.
04 / EXAMPLE
A familiar example
Drawing age → activity and age → health makes the confounding path between activity and health visible.
05 / LIMIT
What it does not mean
The diagram does not automatically discover causal truth; it formalizes knowledge and assumptions that may be wrong.
06 / NOTICE
Notice it in your day
Draw three nodes: age, activity, and health. Add the two arrows from the example and identify the path joining activity to health.
FINAL NOTE
The idea worth keeping
Expose the debatable arrows before choosing controls.
QUESTIONS / 02
Questions people still have
What does an arrow in a DAG represent?
An assumed causal relationship between two variables.
Does the diagram prove its arrows are true?
No. It organizes knowledge and assumptions that may still be wrong.