--- /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}
+ \matrix [draw, below, font=\small, align=center, column sep=2\pgflinewidth, inner sep=0.4em, outer sep=0em, nodes={align=center, anchor=center}] at (current bounding box.south){
+ \node[observed,label=right:observed] {}; \\
+ \node[unobserved,label=right:automatically classified]{}; \\
+ \node[residual,label=right:error term]{}; \\
+ };
+\end{tikzpicture}
+\end{document}
+