DiD-DAG.tex

\documentclass[tikz, border=2pt]{standalone}
% main document, called main.tex
\usepackage{tikz}
\begin{document}

\usetikzlibrary{fit,arrows,calc,positioning,shadows.blur}

\begin{tikzpicture}[var/.style={draw,circle,inner sep=0pt,minimum size=1.2cm},
  latentconf/.style={draw,circle,dashed,inner sep=0pt,minimum size=1.2cm, fill=green!5}
]
  % Nodes
  \node (A) [var] {$A$};
%  \node (A) [var, right=.8cm of Z] {$A$};
    \node (U) [latentconf, above=.8cm of A] {$U$};
    \node (Y) [var, right=.8cm of U] {$Y_1 - Y_0$};
    \node (X) [var, above=.8cm of U] {$X$};
    
    % Arrows
    \path[->, line width=0.5mm]
        (A) edge (Y)
        (U) edge (A)
        (X) edge (Y)
        (U) edge (X)
        (U) edge (Y);
    \path[<->, line width=0.5mm]
        (A) edge[bend left=90, dashed] (U);

\end{tikzpicture}

\end{document}