Mdthbs

How can we draw a continuous vertical line using booktabs in table?
What is the simplest method to maximise the width of a table?
There are lots of methods, very confusing.

documentclass{article}

usepackage{makecell} % for bold in table using small

renewcommandtheadfont{small} % for bold in table using small

usepackage{tabularx, ragged2e} 

usepackage{booktabs}



begin{document}



begin{table}[!ht]

centering

    begin{tabularx}{textwidth}{l>{raggedrightarraybackslash}ccc|ccc}

    toprule

    & multicolumn{3}{c|}{textbf{Paired Differences1}} & multicolumn{3}{c}{textbf{Paired Differences2}}\

     cmidrule{2-7}

    & small {textbf{Statistic}}

     & thead{small {textbf{df}}}

     & thead{small {textbf{Sig.}}}

         & small {textbf{Statistic}}

     & thead{small {textbf{df}}}

     & thead{small {textbf{Sig.}}}    \ 

midrule

    Difference & 44.20 & 14.36 & 4.54 & .957 & 10 & .746\

        bottomrule

    end{tabularx}

caption{Testing Testing Testing%

    label{tab:test1234}% 

    }  

end{table}



end{document}

Here is my suggestion. I have used tabular* in combination with @{extracolsep{fill}} to make the table as wide as the textwidth and to evenly distribute the excess white space between the columns. I have also removed the vertical line and replaced the single cmidrule by two adjacent ones with a small white space inbetween. In order to clean up the code, I have also removed the repeated occurences ot small and textbf and instead added bfseries to thedfont:

documentclass{article}

usepackage{makecell} % for bold in table using small

renewcommandtheadfont{smallbfseries} % for bold in table using small

usepackage{tabularx, ragged2e} 

usepackage{booktabs}



begin{document}



begin{table}[!ht]

    begin{tabular*}{textwidth}{@{extracolsep{fill}}lcccccc}

    toprule

    & multicolumn{3}{c}{textbf{Paired Differences1}} & multicolumn{3}{c}{textbf{Paired Differences2}}\

     cmidrule(r){2-4} cmidrule(l){5-7}

    & thead{Statistic}

     & thead{df}

     & thead{Sig.}

         & thead{Statistic}

     & thead{df}

     & thead{Sig.}    \ 

midrule

    Difference & 44.20 & 14.36 & 4.54 & .957 & 10 & .746\

        bottomrule

    end{tabular*}

caption{Testing Testing Testing%

    label{tab:test1234}% 

    }  

end{table}



end{document}

I would rather replace the vertical line with a supplementary empty column to have a clear separation between the two group of columns. Another possibility, aesthetically, might be to delete the vertical padding of horizontal rules, and replace it with the makegapedcells command from makecell, which adds a vertical space at the top and bottom of all cells. As a demonstration, I replaced the vertical line with thick, light grey vrule, which I find more pleasing to the eye than the default thin, black, vertical rule.

documentclass{article}

usepackage{makecell} % for bold in table using small

renewcommandtheadfont{smallbfseries} % for bold in table using small

usepackage{tabularx, ragged2e}

usepackage{booktabs}

usepackage[table, svgnames]{xcolor}



begin{document}



begin{table}[!ht]

centering

    begin{tabularx}{textwidth}{X>{raggedrightarraybackslash}ccccccc}

    toprule

    & multicolumn{3}{c}{textbf{Paired Differences1}} & & multicolumn{3}{c}{textbf{Paired Differences2}}\

     cmidrule(lr){2-4} cmidrule(lr){6-8}

    & thead{Statistic}

     & thead{df }

     & thead{ Sig. }

      & & thead{Statistic}

     & thead{df}

     & thead{Sig.} \

midrule

    Difference & 44.20 & 14.36 & 4.54 & & .957 & 10 & .746\

        bottomrule

    end{tabularx}

caption{Testing Testing Testing%

    label{tab:test1234}%

    }

end{table}



begin{table}[!ht]

centering

setlength{aboverulesep}{0pt}

setlength{belowrulesep}{0pt}

setcellgapes{3pt}makegapedcells

    begin{tabularx}{textwidth}{X>{raggedrightarraybackslash}ccc!{color{Gainsboro!50!Lavender}vline width 0.75em}ccc}

    toprule

    & multicolumn{3}{c!{color{Gainsboro!50!Lavender}vline width 0.75em}}{textbf{Paired Differences1}} & multicolumn{3}{c}{textbf{Paired Differences2}}\noalign{vskip -0.033em}

     cmidrule(lr{1.33em}){2-4} cmidrule(lr){5-7}

    & thead{Statistic}

     & thead{df}

     & thead{Sig.}

      & thead{Statistic}

     & thead{df}

     & thead{Sig.} \

    noalign{vskip-0.05em}

    cmidrule[0.05em](r{0.9em}){1-4}cmidrule[0.05em](l{0.15em}){5-7}

    Difference & 44.20 & 14.36 & 4.54 & .957 & 10 & .746\

        bottomrule

    end{tabularx}

caption{Testing Testing Testing%

    label{tab:test1234}%

    }

end{table}



end{document} 

With combination of S and X columns type, without vertical lines, with rounded numbers ... :

documentclass{article}

usepackage{booktabs, tabularx}

usepackage{xparse}

NewExpandableDocumentCommandmcx{O{1}m}

    {multicolumn{#1}{>{Centeringsmallbfserieshsize=#1hsize}X}{#2}}

usepackage{ragged2e}

usepackage{siunitx}



begin{document}

    begin{table}[ht]

centering

setlengthtabcolsep{0pt}

sisetup{round-integer-to-decimal,

         round-mode=places,

         table-format=2.2}

    begin{tabularx}{linewidth}{l *{6}{S} }

    toprule

    & mcx[3]{Paired Differences 1} 

    & mcx[3]{Paired Differences 2}             \

    cmidrule(r){2-4}cmidrule(l){5-7}

    & mcx{Statistic}   & mcx{df}  & mcx{Sig.}

    & mcx{Statistic}   & mcx{df}  & mcx{Sig.}    \

    midrule 

Difference 

    & 44.20 & 14.36 & 4.54  & 0.957 & 10     & 0.746 \

        bottomrule

    end{tabularx}

caption{Testing Testing Testing}

label{tab:test1234}

    end{table}

end{document}