--- /dev/null
+\documentclass[12pt]{standalone}
+
+\usepackage{ucs}
+\usepackage[utf8x]{inputenc}
+
+\usepackage[T1]{fontenc}
+\usepackage{textcomp}
+\renewcommand{\rmdefault}{ugm}
+\renewcommand{\sfdefault}{phv}
+\usepackage[garamond]{mathdesign}
+\usepackage{tikz}
+\usetikzlibrary{positioning, shapes, arrows, shadows, }
+
+\begin{document}
+\tikzset{
+ observed/.style={circle, draw},
+ partly observed/.style 2 args={draw, fill=#2, path picture={
+ \fill[#1, sharp corners] (path picture bounding box.south west) -|
+ (path picture bounding box.north east) -- cycle;},
+ circle},
+ unobserved/.style={draw, circle, fill=gray!40},
+ residual/.style={draw, rectangle}
+}
+
+\tikzset{>=latex}
+\begin{tikzpicture}
+
+ \node[observed] (y) {$Y$};
+ \node[unobserved, above=of y] (x) {$X$};
+ \node[observed, left=of x] (w) {$W$};
+
+% \node[unobserved, above=of w] (k) {$K$};
+ \node[observed,right=of x] (z) {$Z$};
+% \node[residual,below=of y] (e) {$\varepsilon$};
+% \node[residual,below=of w] (xi) {$\xi$};
+
+ \draw[->] (z) to (y);
+ \draw[->] (z) -- (x);
+ \draw[->] (x) -- (y);
+ \draw[->] (x) -- (w);
+% \draw[->] (y) -- (w);
+% \draw[->] (x) -- (xi);
+ % \draw[->] (w) -- (xi);
+\end{tikzpicture}
+\end{document}
+