## 2 e-WOM and Online Streaming Content Services  
Studies of eWOM's effects on online service performance outcomes can be divided into two types according to whether product performance is a measure oriented toward consumers (product sales, purchasing intention) or online streaming content service providers (e.g., publication period, product functionalities' enhancement). Previous studies have investigated eWOM's effect on product sales in detail [23; 26; 27; 28; 29]. For example, [PERSON] et al. [26] investigated the influence of online reviews on box office revenue in a designated market area with respect to valence, volume, and variance. [PERSON] and [PERSON] [25] investigated the same effect on product sales and found that they are moderated by product and consumer characteristics. [PERSON] et al. [10] indicated that Facebook \"likes\" influence sales in social commerce, while product and deal characteristics moderate this influence. Finally, [PERSON] and [PERSON] [21] investigated the average number of reviews and the influence of rating on box office revenue.  
Other studies have shown contrasting results of eWOM's effects on sales. For example, while [PERSON] and [PERSON] [18] and [PERSON] et al. [26] showed that review ratings affect product sales significantly, work by [PERSON] et al. [20] indicated that they do not. [PERSON] et al. [17] suggested that consumer expertise and consumer engagement play a crucial moderating role with regard to the influence of social information cues on consumer purchase decisions. [PERSON] and [PERSON] [23] posited that third-party free sampling and external WOM moderate the feedback relationship between internal WOM and sales. While the theory of adverse selection and asymmetric information between buyer and seller can be used to explain online buyers' reliance on eWOM, factors beyond remedying adverse selection and asymmetric information can explain online streaming content service providers' decisions to expand their services.  
eWOM's effects on the performance or quality of online streaming content services, such as online videos, music, and news, have not been studied as much compared to other types of products, such as physical products [13; 30; 31] or movies [20; 26]. Online streaming contents such as webtoons are associated with greater service uncertainty. This is because they are experience goods, and customers must use them for a certain period to develop attitudes about them that affect their decision to continue to purchase them. Service providers also face service uncertainty, in that expanding online streaming content services will not necessarily lead to positive responses from customers. As this uncertainty has reduced the ability to develop this type of online business completely into a legitimate market [10], feedback systems based on eWOM have appeared as a facilitating medium to increase buyers' confidence in purchasing. Previous studies have also suggested that eWOM affects perceived value, willingness to pay, and purchase intention. [PERSON] et al. [32] examined the influence of eWOM on consumers' willingness to pay by assessing its mitigating effects on product and seller uncertainty. [PERSON] et al. [16] suggested that eWOM also affects consumers' perceptions of products' value and their repurchase intentions. [PERSON] et al. [33] also studied eWOM's role in the consumer purchase decision-making process.  
These studies focused on eWOM's effects on consumer-oriented product performance measures, such as sales and purchase intention. However, studies of eWOM's effects on online streaming contents' service performance measures, such as the publication period, or on content enhancement for other businesses (i.e., webtoon gamification), are rare. Accordingly, it is necessary to examine the effects of eWOM on online streaming content service provider-oriented performance measures in this context.