% Source: http://tex.stackexchange.com/a/65518/5645
\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\setlength\PreviewBorder{2mm}
\usepackage{pgfplots}

\begin{document}
\begin{preview}
    \begin{tikzpicture}
        \begin{axis}[/tikz/ybar, % -------- CF
            ybar legend, %-------- CF
            xtick align=outside,% -------- CF
            ymin=0,
            bar width=0.2cm,
            axis x line*=left,
            nodes near coords=\rotatebox{90}{\scriptsize\pgfmathprintnumber\pgfplotspointmeta},
            enlarge x limits=false,
            grid=major,
            height=7cm,
            title={All Results},
            xlabel={bias from reference in \%},
            ylabel={Number of Results},
            symbolic x coords={$<-20$,$-20$,$-19$,$-18$,$-17$,$-16$,$-15$,$-14$,$-13$,$-12$,$-11$,$-10$,$-9$,$-8$,$-7$,$-6$,$-5$,$-4$,$-3$,$-2$,$-1$,$0$,$1$,$2$,$3$,$4$,$5$,$6$,$7$,$8$,$9$,$10$,$11$,$12$,$13$,$14$,$15$,$16$,$17$,$18$,$19$,$20$,$>20$},
            xtick={$-20$,$-15$,$-10$,$-5$,$0$,$5$,$10$,$15$,$20$},
            minor x tick num=4, % ----------- CF
            extra x ticks={$<-20$,$>20$},% ----------- CF
            extra x tick style={xticklabel style={yshift=-15pt}},% ----------- CF
            %xticklabel style={inner sep=0pt, anchor=north east, rotate=45},% ----------- CF
            width=\textwidth]
        \addplot[red,fill=red!40!white] coordinates {($<-20$,3) ($-20$,2) ($20$,0) ($>20$,0)};
        \addplot[yellow,fill=yellow!40!white] coordinates {($-19$,1) ($-18$,2) ($-17$,0) ($-16$,1) ($-15$,0) ($15$,0) ($16$,0) ($17$,0) ($18$,0) ($19$,0)};
        \addplot[blue,fill=blue!40!white] coordinates {($-14$,0) ($-13$,1) ($-12$,1) ($-11$,0) ($-10$,1) ($10$,0) ($11$,1) ($12$,0) ($13$,0) ($14$,1)};
        \addplot[green,fill=green!40!white] coordinates {($-9$,1) ($-8$,5) ($-7$,14) ($-6$,46) ($-5$,105) ($-4$,185) ($-3$,126) ($-2$,297) ($-1$,276) ($0$,301) ($1$,250) ($2$,153) ($3$,67) ($4$,85) ($5$,37) ($6$,29) ($7$,9) ($8$,2) ($9$,10)};
        \legend{Bad,Fair,Good,Excellent}
        \end{axis}
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