*Causal Inference*by Miguel Hernan and Jamie Robins.

In this post, I briefly explore how you can draw DAGs in LaTeX. In the subsequent post, I will show how to draw DAGs using R.

The first example of DAG is the common instrumental variable (IV) setup:

We seek to identify the effect of treatment

*T*on outcome

*Y*. However, this is confounded by an unmeasured variable

*U*. The IV is denoted as

*Z*. Technically, we do not need to put in the crossed out red edges between

*U*and

*Z*and

*Z*and

*Y -*absence of edges encodes independence relations

*.*However, I included them to reinforce (and make explicit) the assumptions needed for identification of causal effects using IVs:

- (Quasi)-exogeneity of the instrument (no path from
*U*to*Z)* - Exclusion restriction (no direct path from
*Z*to*Y*)

This was made using the TikZ package in LaTeX. I used the

`\usepackage{pgf,tikz}`

command at the beginning of my document.
The code to create the DAG above is:

\begin{tikzpicture} % nodes % \node[text centered] (z) {$Z$}; \node[right = 1.5 of z, text centered] (t) {$T$}; \node[right=1.5 of t, text centered] (y) {$Y$}; \node[draw, rectangle, dashed, above = 1 of t, text centered] (u) {$U$}; % edges % \draw[->, line width= 1] (z) -- (t); \draw [->, line width= 1] (t) -- (y); \draw[->,red, line width= 1,dashed] (u) --node {X} (z); \draw[->,line width= 1] (u) --(t); \draw[->,line width= 1] (u) -- (y); \draw[->, red, line width=1,dashed] (z) to [out=270,in=270, looseness=0.5] node{X} (y); \end{tikzpicture}

Note that I first create the nodes (corresponding to variables in the DAG), and then draw the directed edges between the nodes.

Another example of a DAG is a simple structural equation model where we want each edge to be marked with the parameter signifying the causal effect. For example:

In LaTeX:

\begin{tikzpicture} % nodes % \node[text centered] (t) {$T$}; \node[right = 1.5 of t, text centered] (m) {$M$}; \node[right=1.5 of m, text centered] (y) {$Y$}; % edges % \draw[->, line width= 1] (t) -- node[above,font=\footnotesize]{$\beta$} (m); \draw [->, line width= 1] (m) -- node[above,font=\footnotesize]{$\gamma$} (y); \draw[->, line width=1] (t) to [out=270,in=270, looseness=0.5] node[below,font=\footnotesize]{$\delta$} (y); \end{tikzpicture}

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