# Co-Operative Binary Bat Optimizer with Rough Set Reducts for Text Feature Selection
## 5 Results and Discussion
### Internal Evaluation
#### 5.1.3 Statistical Test
The T-test of WRE in the selected generations with BBA\({}_{\text{LHS}}\) and BBA\({}_{\text{CO}}\) is shown in Table 7.  
The results in Table 7 indicate that WRE is significantly higher in the populations of BBA\({}_{\text{CO}}\) until the end of the search process in the Reuters dataset. In the WebKB dataset, WRE remains significantly higher with BBA\({}_{\text{CO}}\) than BBA\({}_{\text{LHS}}\) within the first quarter of the search process. Then, the difference of WRE between both populations of BBA\({}_{\text{CO}}\) and BBA\({}_{\text{LHS}}\) became not significant until later generations. By the end of the search process, WRE of the BBA\({}_{\text{CO}}\) population became significantly higher than that of BBA\({}_{\text{LHS}}\) population. The reason behind that is that the populations of BBA\({}_{\text{CO}}\) are more diverse, and thus, the solutions are more distributed in the search space until the later generations. In contrast, the solutions of BBA\({}_{\text{LHS}}\) population in the later generations are found to be closer to each other. In this way, the quality of the worst solution with BBA\({}_{\text{LHS}}\) remains better than the one with BBA\({}_{\text{CO}}\) in Reuters dataset. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dataset** & \multicolumn{2}{c}{**Reuters**} & \multicolumn{2}{c}{**WebKB**} \\ \hline
**Method** & **BBA\({}_{\text{CO}}\)** & **BBA\({}_{\text{LHS}}\)** & **BBA\({}_{\text{CO}}\)** & **BBA\({}_{\text{LHS}}\)** \\ \hline \multicolumn{5}{c}{generation 1} \\ \hline Mean & 35.83 & 31.96 & 47.16 & 34.30 \\ \(p\)-Value & 0.63 & 0.39 & 0.08 & 0.15 \\ \(t\) State & 2.11 & & 18.56 & \\ \(t\) Critical two-tail & 2.03 & & 2.03 & \\ \hline \multicolumn{5}{c}{generation 20} \\ \hline Mean & 24.03 & 20.50 & 23.75 & 23.50 \\ \(p\)-Value & 0.79 & 0.38 & 0.13 & 0.15 \\ \(t\) State & 3.14 & & 0.21 & \\ \(t\) Critical two-tail & 2.03 & & 2.01 & \\ \hline \multicolumn{5}{c}{generation 50} \\ \hline Mean & 20.42 & 20.00 & 21.86 & 23.37 \\ \(p\)-Value & 0.72 & 0.25 & 0.42 & 0.27 \\ \(t\) State & 0.45 & & \(-1.04\) & \\ \(t\) Critical two-tail & 2.03 & & 2.00 & \\ \hline \multicolumn{5}{c}{generation 80} \\ \hline Mean & 14.80 & 18.50 & 18.98 & 21.50 \\ \(p\)-Value & 0.54 & 0.29 & 0.36 & 0.16 \\ \(t\) State & \(-7.24\) & & \(-3.22\) & \\ \(t\) Critical two-tail & 2.01 & & 2.04 & \\ \hline \multicolumn{5}{c}{generation 100} \\ \hline Mean & 14.60 & 18.50 & 15.89 & 21.00 \\ \(p\)-Value & 0.84 & 0.27 & 0.45 & 0.19 \\ \(t\) State & \(-4.57\) & & \(-7.05\) & \\ \(t\) Critical two-tail & 2.02 & & 2.03 & \\ \hline \end{tabular}
\end{table} 
Table 5: The \(t\)-test of BRE in different generations using BBA\({}_{\text{CO}}\) and BBA\({}_{\text{LHS}}\). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dataset** & \multicolumn{2}{c}{**Reuters**} & \multicolumn{2}{c}{**WebKB**} \\ \hline
**Method** & \(\mathbf{BBA_{CO}}\) & \(\mathbf{BBA_{LHS}}\) & \(\mathbf{BBA_{CO}}\) & \(\mathbf{BBA_{LHS}}\) \\ \hline \multicolumn{5}{c}{generation 1} \\ \hline Mean & 90.85 & 86.90 & 90.72 & 86.78 \\ \(p\)-Value & 0.14 & 0.38 & 0.40 & 0.16 \\ \(t\) State & 7.45 & & 3.50 & \\ \(t\) Critical two-tail & 2.00 & & 2.02 & \\ \hline \multicolumn{5}{c}{generation 20} \\ \hline Mean & 87.91 & 86.25 & 88.00 & 85.24 \\ \(p\)-Value & 0.18 & 0.21 & 0.32 & 0.06 \\ \(t\) State & 1.88 & & 2.51 & \\ \(t\) Critical two-tail & 2.03 & & 2.00 & \\ \hline \multicolumn{5}{c}{generation 50} \\ \hline Mean & 84.73 & 85.61 & 84.00 & 81.65 \\ \(p\)-Value & 0.09 & 0.19 & 0.10 & 0.13 \\ \(t\) State & \(-0.90\) & & 1.86 & \\ \(t\) Critical two-tail & 2.00 & & 2.00 & \\ \hline \multicolumn{5}{c}{generation 80} \\ \hline Mean & 78.07 & 68.95 & 75.12 & 79.15 \\ \(p\)-Value & 0.17 & 0.32 & 0.07 & 0.16 \\ \(t\) State & 6.88 & & \(-2.00\) & \\ \(t\) Critical two-tail & 2.02 & & 2.00 & \\ \hline \multicolumn{5}{c}{generation 100} \\ \hline Mean & 74.52 & 62.95 & 70.85 & 77.64 \\ \(p\)-Value & 0.24 & 0.14 & 0.21 & 0.08 \\ \(t\) State & 5.64 & & \(-2.84\) \\ \(t\) Critical two-tail & 2.00 & & 2.02 & \\ \hline \hline \end{tabular}
\end{table}