\begin{table}[!htbp] \centering
  \caption{Explaining how many pledges parties make}
  \label{}
\small
\begin{tabular}{@{\extracolsep{5pt}}lcccc}
\\[-1.8ex]\hline
\hline \\[-1.8ex]
 & \multicolumn{4}{c}{\textit{Dependent variable:}} \\
\cline{2-5}
\\[-1.8ex] & \multicolumn{4}{c}{Number of pledges} \\
\\[-1.8ex] & Model 1 & Model 2 & Model 3 & Model 4 \\
\hline \\[-1.8ex]
 Length (log) & 63.962$^{***}$ (8.905) & 62.014$^{***}$ (9.147) &  &  \\
  Length (absolute) &  &  & 0.056$^{***}$ (0.009) & 0.056$^{***}$ (0.009) \\
  Growth \textsuperscript{t-1} & $-$11.551$^{***}$ (4.346) & $-$10.083$^{**}$ (4.565) & $-$10.584$^{**}$ (4.492) & $-$11.045$^{**}$ (4.634) \\
  Opposition & $-$60.542$^{*}$ (31.895) & $-$0.686 (15.483) & $-$47.030 (33.063) & $-$0.545 (15.688) \\
  Extremism & $-$12.387$^{*}$ (6.416) &  & $-$7.888 (6.677) &  \\
  Ideology &  & $-$0.401 (0.493) &  & $-$0.673 (0.499) \\
  Issue diversity & 3.816$^{**}$ (1.789) & 3.681$^{**}$ (1.797) & 6.383$^{***}$ (1.793) & 6.015$^{***}$ (1.760) \\
  Vote share \textsuperscript{t-1} & $-$0.286 (0.387) & $-$0.089 (0.395) & $-$0.153 (0.402) & 0.029 (0.400) \\
  Year (from 1950) & 1.109 (1.074) & 1.246 (1.106) & 2.043$^{*}$ (1.068) & 2.162$^{**}$ (1.069) \\
  Growth x Opposition & 13.414$^{**}$ (5.180) & 12.100$^{**}$ (5.465) & 12.948$^{**}$ (5.358) & 13.005$^{**}$ (5.555) \\
  Extremism x Opposition & 15.914$^{**}$ (7.263) &  & 12.770$^{*}$ (7.534) &  \\
  Ideology x Opposition &  & 0.060 (0.593) &  & 0.216 (0.602) \\
  Constant & $-$350.367$^{***}$ (65.884) & $-$389.618$^{***}$ (61.557) & $-$109.818$^{*}$ (60.609) & $-$139.487$^{**}$ (54.446) \\
 \hline \\[-1.8ex]
Observations & 111 & 111 & 111 & 111 \\
R$^{2}$ & 0.767 & 0.760 & 0.750 & 0.754 \\
Adjusted R$^{2}$ & 0.724 & 0.716 & 0.705 & 0.709 \\
Residual s.e. & 45.428 & 46.084 & 47.016 & 46.693 \\
\hline
\hline \\[-1.8ex]
\textit{Note:}  & \multicolumn{4}{r}{$^{*}$p$<$0.1; $^{**}$p$<$0.05; $^{***}$p$<$0.01} \\
\end{tabular}
\end{table}