## 5 Discussion
### Promotion of Speech Level Shift  
The formal style rate in the user utterances tended to be similar to that of the dialog system. Thus, we analyzed the dialog logs between the participants and the dialog system, with a focus on the conditions in which the speech level was shifted. Table 3 presents the dialog logs as an example of a successful dialog with the formal style rate (26.67%) that was closest to that of the BTSJ Japanese natural conversation corpus for the core conversation during the first meeting. At the beginning of the dialog, both the user and dialog system used a formal style; however, the dialog system shifted its speech level to an informal style at the fifth utterance (bolded part). From the fifth to eleventh utterances, the user continuously spoke in an informal style, and the dialog system used an informal style to match the user. We observed a case in which the users also shifted their speech level in response to a speech level shift in the dialog system. In this dialog example, the speech level was shifted from a formal style to an informal style, and thus, the dialog was conducted so that the user and dialog system reduced their psychological distance. An example of inappropriate dialog is shown in Table 4. In this example, the dialog system does not provide appropriate responses to the user's questions and opinions. Because the dialog system used in this experiment is rule-based, it cannot generate flexible responses to the user's questions or to the development of new topics, which is a weakness of the system. However, the results presented in Figure 3 show that this experiment succeeded in giving the user the impression that the dialog was appropriate.  
In 19 (41.3%) of the logs, the user changed their speech level within two turns, according to the speech level of the dialog system. According to these results, the speech level shift of the dialog system successfully encouraged several users to shift their speech level. Furthermore, we investigated the correlation between the impression evaluation value and the number of speech level shifts. We conducted a correlation analysis with the evaluation values of Q4, Q5, and Q6 for 46 experimental participants in the speech level shift condition. No significant correlation was found with any of the impression evaluation items (Q4: correlation coefficient (\(r\)) = 0.21, Q5: \(r\ =\ 0.03\), and Q6: \(r\ =\ 0.02\), \(ps>0.1\)). These results suggest that awareness of dialog system speech level shifts does not necessarily lead to an increased frequency of user speech level shifts.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Speaker** & **Utterances** \\ \hline \multirow{3}{*}{U6} & Tokyo ni itte mitai desu ga, Tokyo tke kankochi to iu kanji ga amari shimasen \\  & yo ne? (I would like to visit Tokyo, but it doesn’t really give off the vibe of a \\  & tourist destination, does it?) \\ \hline \multirow{2}{*}{S7} & Fumu... itsu goro ikou toka tte arimasu ka? (Hmm... do you have any plans \\  & on when you might go?) \\ \hline \multicolumn{2}{l}{(Omission)} \\ \hline \multirow{3}{*}{U8} & Keshiki o miru no mo ii desu ga, watashi wa gotochi gurume mo tanoshimi ni \\  & shiteimasu. (While enjoying the scenery is nice, I’m also looking forward to \\  & trying local cuisine.) \\ \hline \multirow{3}{*}{S9} & Demo ryokó to ieba oishii gohan mo sute-gatai desu yo ne... Nanika osusume \\  & no gohan te arum desu ka? (But when it comes to traveling, delicious food is \\  & irresistible, right? Do you have any recommended dishes?) \\ \hline \hline \end{tabular}
\end{table}
Table 4: An example where the dialog system was unable to provide appropriate responses to the user’s questions or opinions. S = system and U = user (participant).