## 2 Research Background and Hypothesis Development
### Research Model and Hypothesis Development  
Based on the literature review, we developed the research model shown in Figure 1. As mentioned above, based on the cognitive bias model, personality traits (for example, generalized trust (from [PERSON] and [PERSON] [14]), self-consciousness and friendship (from [PERSON] and [PERSON] [17]), and desire for self-presentation and admiration (from [PERSON] and [PERSON] [17])) would have direct effects on SWB (blue line). Additionally, as depression tendency (from [PERSON] and [PERSON] [17]), social support (from [PERSON] and [PERSON] [14]) (purple line), anxiety toward COVID-19 (green line), and usage of the Internet and social media (from [PERSON] et al. [16]) (orange line) are also related to SWB, we included these factors in our research model. Given the significant changes in the social environment surrounding COVID-19, we anticipated that axieties related to the pandemic would gradually decrease, leading to a progressively weaker impact on SWB over time. As social media use patterns interact with these effects [16; 17], we explored the social network mediation model by combining these factors with social media use patterns and their influence on SWB (dashed lines refer to these factors' effects). Based on the conceptual model proposed by [PERSON] et al. [7], the motives for using different social media patterns (i.e., what social media the participants used) can be mapped back to their proposed activities, motives, and communication partners (arrow refers to mediating effects). Therefore, we propose the following hypotheses based on different patterns of social media use: As stated earlier, the three most popular social media in Japan are LINE, Twitter, and Instagram; we used the pattern of LINE + Twitter + Instagram as the basis. Additionally, because Discord and TikTok are the fourth and fifth most popular platforms, we focused on the use of (1) LINE + Twitter + Instagram + Discord and (2) LINE + Twitter + Instagram+ TikTok, respectively.  
Figure 1: Research model.  
**H1.**: _Users of LINE + Twitter + Instagram have the lowest levels of anxiety toward COVID-19 and depression tendency because they connect with and receive support from the most intimate others, leading to the highest SWB levels._
**H2.**: _Compared to LINE + Twitter + Instagram users, LINE + Twitter + Instagram + TikTok users have higher levels of anxiety toward COVID-19 and depression tendency because they connect with and receive less social support from fewer intimate others, leading to lower SWB levels._
**H3.**: _Compared to the other two groups of users, users of LINE + Twitter + Instagram + Discord have the highest levels of anxiety toward COVID-19 and depression tendency because they connect with the fewest intimate others, leading to the lowest SWB levels._
**H4.**: _As the self-consciousness of friendship and desire for self-presentation and admiration are more obvious under the condition of visual anonymity, their effects will be more obvious among users of LINE + Twitter + Instagram + Discord, followed by users of LINE + Twitter + Instagram + TikTok and LINE + Twitter + Instagram. However, because all three groups connect with intimate and non-intintinate others on different social media platforms, their levels of generalized trust will be the same among the three groups, which will have the same effect on their SWB levels._
**H5.**: _Users of LINE + Twitter + Instagram have the highest level of OCSs and the largest effect on SWB, followed by users of LINE + Twitter + Instagram + TikTok and users of LINE + Twitter + Instagram + Discord._  
Previous studies have shown that male students prefer Discord, whereas female students prefer Instagram and TikTok, with no differences in LINE or Twitter use (e.g., [26]). Therefore, we propose the following hypothesis:  
**H6.**: _There are differences between male students in the LINE + Twitter + Instagram + Discord group and female students in the LINE + Twitter + Instagram + TikTok group in the above five hypotheses._