How can I center my table in the middle of a two-column document?

Question

I want to center my table in the middle of a two-column document in Latex. I have tried the {table*} and "\centering" command and it works, but not completely. It left aligns the table instead of centering it across the two columns. Here is my code. I would appreciate any tips on how to center this table properly.

\begin{table*}
\centering
\caption{Monte Carlo Simulation Results vs. Historical Food Distributions}
\label{table:DistributionComparison}
\begin{tabular}{@{}llllcll@{}}
\toprule
\multicolumn{2}{l}{Simulation} & \multicolumn{2}{l}{Historical} & Difference between means &        &                  \\ \midrule
$M_1$            & $(SD_1)$           & $M_2$             & $(SD_2)$            & $M_1$ - $M_2$ {[}95\% CI{]}    & $t(460)$  & $p$                \\ \midrule
146,797          & (3,786)          & 122,468           & (27,411)           & 24,330 {[}21,080, 27,578{]}    & 14.7132  & \textless{}0.001 \\
\bottomrule
\end{tabular}
\begin{tablenotes}
\small
\item Note. $ N=462$. CI = Confidence Interval; $n_1 = 450$. $n_2 = 12$. 
\end{tablenotes}
\end{table*}

Answer 1

You haven't provided the full code to compile and test so I am guessing the annotation are moved left because table itself should be centred.

First, the table* environment creates space of the full width but your table is is not that wide. I never used tablesnotes this way and I guess because it is not a part of the table, it is moved to the left margin with a small indentation as tablesnotes create a list.

If you want annotation to be aligned with the table, remove tablesnotes and either insert one more row below \bottomrule with all cells merged

 \multicolumn{7}{@{}l}{\small Note. ...}

or apply threeparttable as in the example below, which I would recommend

\documentclass[twocolumn]{article}
\usepackage{booktabs}
\usepackage{threeparttable}
\usepackage{kantlipsum}

\begin{document}
\kant[1-4]

\begin{table*}
  \centering
  \begin{threeparttable}
    \caption{Monte Carlo Simulation Results vs. Historical Food Distributions}
    \label{table:DistributionComparison}
    \begin{tabular}{@{}llllcll@{}}
      \toprule
      \multicolumn{2}{c}{Simulation}
      & \multicolumn{2}{c}{Historical}
      & Difference between means
      & & \\
      \midrule
      $M_1$   & $(SD_1)$ & $M_2$   & $(SD_2)$ & $M_1$ - $M_2$ {[}95\% CI{]} & $t(460)$ & $p$ \\
      \midrule
      146,797 & (3,786)  & 122,468 & (27,411) & 24,330 {[}21,080, 27,578{]} & 14.7132  & $<0.001$ \\
      \bottomrule
    \end{tabular}
    {\small Note. $ N=462$. CI = Confidence Interval; $n_1 = 450$. $n_2 = 12$.}
  \end{threeparttable}
\end{table*}

\kant[2-5]
\end{document}

Answer 2

Like this?

With taltblr table, which is tabularray equivalent for threeparttable and use of the stfloat package, you can get table centered at the top or at the bottom of the page (if it is inserted in the first column and after this point is enough space for table):

\documentclass[twocolumn]{article}
\usepackage{stfloats}
\usepackage{tabularray}
\UseTblrLibrary{booktabs}
\usepackage{lipsum}

\begin{document}
\lipsum[1-2]

\begin{table*}[b]
  \centering
    \begin{talltblr}[
caption = {Monte Carlo Simulation Results vs. Historical Food Distributions},
  label = {table:DistributionComparison},
note{} = {Note: $ N=462$, CI = Confidence Interval, $n_1 = 450$, $n_2 = 12$.}
                    ]{colspec = {@{} *{7}{Q[c, mode=math]} @{}},
                      row{1}  = {c, mode=text}
                      }
    \toprule
\SetCell[c=2]{c}   Simulation 
    &   &   \SetCell[c=2]{c}   Historical 
            &   &   Difference between means
                    &   &   \\
    \cmidrule[r]{1-2}
    \cmidrule[lr]{3-4}
    \cmidrule[lr]{5-5}
M_1     & (SD_1)    & M_2       & (SD_2)    & M_1 - M_2\ [95\,\% CI]    & t(460)    & p \\
    \midrule
146,797 & (3,786)   & 122,468   & (27,411)  & 24,330\ [21,080, 27,578]  & 14.7132   & <0.001 \\
146,797 & (3,786)   & 122,468   & (27,411)  & 24,330\ [21,080, 27,578]  & 14.7132   & <0.001 \\
      \bottomrule
    \end{talltblr}
\end{table*}

\lipsum[3-6]
\end{document}