## 3 Results and Discussions
### Order Picking Performance
#### 3.2.2 Performance of Solutions Technology  
Voice picking technology is far the most competitive overall (see Table 6). Except in one case, voice picking is present in all of the subsets. This result indicates that voice picking technology contributes more to the efficiency of order picking systems irrespective of the warehouse configuration and routing policy. The voice picking has an edge over the handheld devices because confirmation  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Warehouse** & **0** \({}^{\text{a}}\) & **0.01** & **0.02** & **0.03** & **0.04** & **0.05** & **Total** \\ \hline \multicolumn{8}{c}{Midpoint} \\ \hline Barcode Handheld & 1 & & & \(\surd\) & & & 1 \\ Voice picking & 1 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & 6 \\ Voice picking & 2 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & 6 \\ Voice picking & 3 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & 6 \\ Voice picking & 4 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & 6 \\ \hline  & 4 & 4 & 5 & 4 & 4 & 4 & 25 \\ \hline Average Efficiency & 0.97 & 0.97 & 0.96 & 0.96 & 0.95 & 0.96 & 0.96 \\ \hline \multicolumn{8}{c}{Return} \\ \hline Voice picking & 1 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & 6 \\ Voice picking & 3 & \(\surd\) & \(\surd\) & & \(\surd\) & \(\surd\) & \(\surd\) & 5 \\ \hline  & 2 & 2 & 1 & 2 & 2 & 2 & 11 \\ \hline Average Efficiency & 0.92 & 0.92 & 0.94 & 0.91 & 0.90 & 0.91 & 0.91 \\ \hline \multicolumn{8}{c}{Traversal} \\ \hline Voice picking & 1 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & 6 \\ Voice picking & 2 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & 6 \\ Voice picking & 3 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & 6 \\ Voice picking & 4 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & 6 \\ \hline  & 4 & 4 & 4 & 4 & 4 & 4 & 24 \\ \hline Average Efficiency & 0.97 & 0.99 & 0.98 & 0.97 & 0.96 & 0.97 & 0.97 \\ \hline \hline \end{tabular} Note: \({}^{\text{a}}\) The standard deviation of the error probabilities, given a normal distribution.  
\end{table}
Table 7: Sensitivity analysis of the effect of error on the order picking performance.  
activity is done during picking and therefore takes a shorter time to process orders. Error costs are therefore relatively lower for voice picking technology. When handheld without \(e_{3}\) or \(e_{4}\) and voice picking with errors are evaluated, voice picking technology still outperforms the handheld devices (sixth and eighth columns in Table 6). However, a further analysis of the picking errors effect shows that handheld without propagating errors and voice picking with errors equally perform (10 th column in Table 6). This shows that only when handheld devices are propagating errors free that they can perform as well as voice picking technologies. Therefore, reducing propagating errors can play a significant role in enhancing order picking efficiency. Reducing propagating errors leads to less travel time and higher service level. Given that voice picking technologies are more expensive, decision makers can reduce the operating cost by implementing handheld technologies and at the same time eliminating or reducing propagation errors.