# Understanding Query Combination Behavior in Exploratory Searches
## 3 A Hierarchy of Query Combination Behavior
### Successful vs. Unsuccessful QCB  
We now turn our attention to understanding the role QCB play in the exploratory search process, to know, for example, whether users can find their required information by performing QCB. This is important because methods should be designed to help users combine queries if most users benefit from QCB. Conversely, if QCB blocks users' exploratory processes, search engines should avoid users combining queries. For this purpose, we began by identifying the success of QCB, as follows:  
* Successful: QCB sessions where users can find their required information by issuing CBQs.
* Unsuccessful: QCB sessions where searchers failed to find the required information by issuing CBQs.  
These criteria are inspired by [PERSON]'s study [26]. After labeling, participants were asked to answer the following question, if a QCB was judged as \"successful\":  
* Do you think CPQ should be issued if the user issues CBQ in advance? Select \"Yes\" or \"No\".  
In addition, participants were asked to answer the following question, if a QCB was judged as \"unsuccessful\":  
* Why do you think the user failed to succeed by issuing CBQ? Describe what you think made this QCB fail in one sentence.  
The distribution of \"successful\" and \"unsuccessful\" searches is shown in Table 1. The table shows that most of the QCB were successful (more than 86%). We also found that 43% of users completed their search processes after issuing CBQs. In addition, most QCB were \"successful\" for each of the 3 QCB categories (the lowest was more than 75% for the query diversification category). These findings suggest that users can find their required information by exhibiting QCB.  
Figure 4 shows the distribution of the judgments of the question when QCB was judged as \"successful\". It is observed from Figure 4 that most (more than 88%) users can find their required information by issuing CBQ without issuing CPQ, providing strong evidence that prompting users to combine queries can help them to complete their search task quickly.  
In addition, Table 2 summarizes the top three mentioned reasons which make QCB \"unsuccessful\". About 54% of QCB were judged as \"unsuccessful\" because users explored the wrong search objects in the topic. This highlights that accurate identification of user information requirements is helpful for these users. We also notice that about 11% of \"unsuccessful\" searches were judged as such because users issued invalid combinations;  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Total** & \begin{tabular}{c} **Topic** \\ **Specialization** \\ \end{tabular} & \
\begin{tabular}{c} **Relation** \\ **Discovery** \\ \end{tabular} &
\begin{tabular}{c} **Query** \\ **Diversification** \\ \end{tabular} \\ \hline Successful & 86\% & 88\% & 86\% & 75\% \\ Unsuccessful & 14\% & 12\% & 14\% & 25\% \\ \hline \hline \end{tabular}
\end{table}
Table 1: Distribution of “successful” and “unsuccessful” searches.  
Figure 4: Distribution of “Yes” and “No” in answering the question “Do you think CPQ should be issued if the user issues CBQ in advance? “.  
this is where users combine queries for unknown reasons, for example, the QCB session \(<\)\"fire\", \"flame\", \"fire flame\"\(>\), with all kinds of unrelated clicks. We suspect that these users may randomly combine queries together, or forget to delete the previously issued terms when reissuing a query.