Answer by egreg for change font for content of table

Just remove $ where unneeded (that is, almost everywhere).

\documentclass{article}\usepackage{booktabs}\usepackage{etoolbox}\usepackage[format=plain,  labelformat=simple,  font={small,sf,bf},  indention=0cm,  labelsep=period,  justification=centering,  singlelinecheck=true,  tableposition=top,  figureposition=bottom,]{caption}\makeatletter\appto\@floatboxreset{%  \ifx\@captype\andy@table    \ttfamily  \fi}\def\andy@table{table}\makeatother\begin{document}Blah blah. Should be a serif font.\begin{table}\centering\caption{My title}\label{m123}% fix the overfull\small\addtolength{\tabcolsep}{-2pt}\begin{tabular}{ l c c c }\hline& treat x time & treat x time x female & treat x time x female \\\hline(Intercept) & -0.03         & 0.01          & -0.83$^{*}$    \\& [-0.16; 0.10] & [-0.13; 0.15] & [-0.93; -0.73] \\v1          & -0.06         & -0.06         & -0.07          \\& [-0.23; 0.11] & [-0.23; 0.11] & [-0.18; 0.05]  \\v2          & 0.05          & -0.03         &                \\& [-0.04; 0.15] & [-0.16; 0.11] &                \\\hline\multicolumn{4}{l}{%  \scriptsize $^*$ 0 outside the confidence interval. Fixed effect of time treated as factor.%}\end{tabular}\end{table}Blah blah. Should be a serif font.\end{document}

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Some further notes.

1. Place the \label next to the object it refers to, in this case the \caption

2. \scriptsize does not take an argument.

3. Don't use center in a table environment, but \centering.

If you don't want to touch the table as generated by the external program, it's a bit more difficult.

\documentclass{article}\usepackage{booktabs}\usepackage{etoolbox}\usepackage[format=plain,  labelformat=simple,  font={small,sf,bf},  indention=0cm,  labelsep=period,  justification=centering,  singlelinecheck=true,  tableposition=top,  figureposition=bottom]{caption}\makeatletter\appto\@floatboxreset{%  \ifx\@captype\andy@table    \ttfamily    \everymath{\fam=\group@mathtt\relax\andy@changemathcodes}%  \fi}\def\andy@table{table}\let\andy@space\ %\AtBeginDocument{%  \check@mathfonts  \sbox\z@{$\mathtt{\xdef\group@mathtt{\gdef\noexpand\group@mathtt{\the\fam}}\group@mathtt}$}%  \def\andy@changemathcodes{%    \count@="2\group@mathtt00 \advance\count@`-\mathcode`-=\count@    \count@="4\group@mathtt00 \advance\count@`[\mathcode`[=\count@    \count@="5\group@mathtt00 \advance\count@`]\mathcode`]=\count@    \count@="0\group@mathtt00 \advance\count@`;\mathcode`;=\count@    \def\ {\mathopen{\andy@space}}%  }%}\makeatother\begin{document}Blah blah. Should be a serif font; here's math: $a+b$\begin{table}\centering\caption{With dollars}% fix the overfull\small\addtolength{\tabcolsep}{-2pt}\begin{tabular}{ l c c c }\hline& treat x time & treat x time x female & treat x time x female       \\\hline(Intercept) & $-0.03$          & $0.01$           & $-0.83^{*}$       \\& $[-0.16;\ 0.10]$ & $[-0.13;\ 0.15]$ & $[-0.93;\ -0.73]$ \\v1          & $-0.06$          & $-0.06$          & $-0.07$           \\& $[-0.23;\ 0.11]$ & $[-0.23;\ 0.11]$ & $[-0.18;\ 0.05]$  \\v2          & $0.05$           & $-0.03$          &                   \\& $[-0.04;\ 0.15]$ & $[-0.16;\ 0.11]$ &                   \\\hline\multicolumn{4}{l}{%  \scriptsize$^*$ 0 outside the confidence interval. Fixed effect of time treated as factor.%}\end{tabular}\end{table}\begin{table}[htp]\centering\caption{My title}\label{m123}% fix the overfull\small\addtolength{\tabcolsep}{-2pt}\begin{tabular}{ l c c c }\hline& treat x time & treat x time x female & treat x time x female \\\hline(Intercept) & -0.03         & 0.01          & -0.83$^{*}$    \\& [-0.16; 0.10] & [-0.13; 0.15] & [-0.93; -0.73] \\v1          & -0.06         & -0.06         & -0.07          \\& [-0.23; 0.11] & [-0.23; 0.11] & [-0.18; 0.05]  \\v2          & 0.05          & -0.03         &                \\& [-0.04; 0.15] & [-0.16; 0.11] &                \\\hline\multicolumn{4}{l}{%  \scriptsize $^*$ 0 outside the confidence interval. Fixed effect of time treated as factor.%}\end{tabular}\end{table}Blah blah. Should be a serif font; here's math: $a+b$.\end{document}

As you see, the output is the same.

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