I used proposed code in How to construct a confusion matrix in LaTeX? to create a confusion matrix:
\documentclass{article}
\usepackage{array}
\usepackage{graphicx}
\usepackage{multirow}
\newcommand\MyBox[2]{
\fbox{\lower0.75cm
\vbox to 1.7cm{\vfil
\hbox to 1.7cm{\hfil\parbox{1.4cm}{#1\\#2}\hfil}
\vfil}%
}%
}
\begin{document}
\noindent
\renewcommand\arraystretch{1.5}
\setlength\tabcolsep{0pt}
\begin{tabular}{c >{\bfseries}r @{\hspace{0.7em}}c @{\hspace{0.4em}}c @{\hspace{0.7em}}l}
\multirow{10}{*}{\rotatebox{90}{\parbox{1.1cm}{\bfseries\centering actual\\ value}}} &
& \multicolumn{2}{c}{\bfseries Prediction outcome} & \\
& & \bfseries p & \bfseries n & \bfseries total \\
& p$'$ & \MyBox{True}{Positive} & \MyBox{False}{Negative} & P$'$ \\[2.4em]
& n$'$ & \MyBox{False}{Positive} & \MyBox{True}{Negative} & N$'$ \\
& total & P & N &
\end{tabular}
\end{document}

This is a little big for my two columns article. How can I decease (scale) size of it?
Ps.
I'm using \documentclass[conference,hidelinks]{IEEEtran} as document class.

twocolumnto the\documentclassinstruction of your example code, the matrix fits perfectly well in the available space. Upshot: please indicate in more detail how you set up two-column mode for your document. – Mico Apr 08 '15 at 13:31\documentclass[conference,hidelinks]{IEEEtran}is documentclass that I'm using. – user2991243 Apr 08 '15 at 13:33IEEEtrandocument class. Please consider posting a screenshot to illustrate more clearly what the problem is. – Mico Apr 08 '15 at 13:38graphicxpackage, you could use that package's\scaleboxmacro to scale down the confusion matrix. Start with\scalebox{0.8}{<code for confusion matrix>}. – Mico Apr 08 '15 at 13:54\scalebox. + adding caption and label to it. thanks. – user2991243 Apr 08 '15 at 14:05\scalebox. I'm afraid I'm a dreadful psychic; I thus won't venture a guess as to what the appropriate arguments for\captionand\labelmay be. I trust you can figure out on your own how to provide these instructions. – Mico Apr 08 '15 at 14:16