Q:

PGFPlots error bars with coordinate values from table

I have a table of estimated averages and their associated confidence intervals. But when I plot the confidence intervals, pgfplots treats the interval coordinates as error values. Is there a way to tell pgfplots to plot the CI data as is, instead of adding/subtracting the CI values from the mean? 
MWE
\documentclass[border=2pt]{standalone} 
\usepackage{pgfplots}
\usepackage{filecontents}
\begin{filecontents*}{data.txt}
Round   NUM CI-L    CI-H    
1   1.50    1.09    1.91    
2   1.05    0.61    1.49    
3   0.50    0.14    0.86    
4   0.20    -0.03   0.43    
5   0.35    -0.15   0.85    
6   0.30    -0.05   0.65    
7   0.20    -0.10   0.50    
8   0.25    -0.15   0.65    
9   0.20    -0.10   0.50    
10  0.20    -0.10   0.50    
11  0.15    -0.06   0.36    
12  0.20    -0.10   0.50    
13  0.20    -0.10   0.50    
14  0.20    -0.10   0.50    
15  0.20    -0.10   0.50    
16  0.25    -0.15   0.65    
17  0.15    -0.06   0.36    
18  0.20    -0.10   0.50    
19  0.20    -0.10   0.50    
20  0.15    -0.06   0.36    
\end{filecontents*}

\begin{document}

\begin{tikzpicture}
\begin{axis}
\addplot table [x index=0, y index=1] {data.txt};
\addplot[error bars/.cd,y dir=minus,y explicit] table [x index=0, y index=1,y error index=2] {data.txt};
\addplot[error bars/.cd,y dir=plus,y explicit] table [x index=0, y index=1,y error index=3] {data.txt};
\end{axis}
\end{tikzpicture}

\end{document}

Output

A:

This can be done using y error plus expr and y error minus expr keys. Also you can combine all the three \addplot commands to one.
\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
\usepackage{filecontents}
    \begin{filecontents*}{data.txt}
        Round   NUM CI-L    CI-H
        1   1.50    1.09    1.91
        2   1.05    0.61    1.49
        3   0.50    0.14    0.86
        4   0.20    -0.03   0.43
        5   0.35    -0.15   0.85
        6   0.30    -0.05   0.65
        7   0.20    -0.10   0.50
        8   0.25    -0.15   0.65
        9   0.20    -0.10   0.50
        10  0.20    -0.10   0.50
        11  0.15    -0.06   0.36
        12  0.20    -0.10   0.50
        13  0.20    -0.10   0.50
        14  0.20    -0.10   0.50
        15  0.20    -0.10   0.50
        16  0.25    -0.15   0.65
        17  0.15    -0.06   0.36
        18  0.20    -0.10   0.50
        19  0.20    -0.10   0.50
        20  0.15    -0.06   0.36
    \end{filecontents*}
\begin{document}
    \begin{tikzpicture}
        \begin{axis}[
        ]
            \addplot+ [
                error bars/.cd,
                    y explicit,
                    y dir=both,
            ] table [
                x=Round,
                y=NUM,
                y error plus expr=\thisrow{CI-H}-\thisrow{NUM},
                y error minus expr=\thisrow{NUM}-\thisrow{CI-L},
            ] {data.txt};
        \end{axis}
    \end{tikzpicture}
\end{document}

