## 2 Literature Review
### [PERSON]'s Model  
[PERSON]'s model is one of the techniques used to study consumer demand and is based on the principle that consumer satisfaction with the product is strongly related to the ability to meet consumers' needs. The consumer must achieve the highest satisfaction with the defect that causes the consumer's least dissatisfaction. Customer satisfaction has often been seen as one-dimensional, which means that when the quality elements are sufficient, people feel satisfied (and vice versa); however, in reality, not all quality factors are the same [27; 28]. [PERSON] et al. [29] proposed a two-dimensional quality model that pointed out that the customer's \"satisfaction\" and \"quality attributes\" are not completely linearly related. Whenthe quality factors are sufficient, it may not make people feel satisfied, and sometimes it will cause dissatisfaction or unsatisfactory results; or when a certain aspect of the service does not meet the customers' expectations, it can result in dissatisfaction. However, after improving these quality factors, there is no significant improvement in the satisfaction of consumers. It can be inferred that the quality attributes that affect consumer satisfaction or dissatisfaction are different. [PERSON] and [PERSON] [30] also pointed out that quality factors may cause customers to be dissatisfied or indifferent. [PERSON]'s model classifies quality into five attributes [29; 31], which are attractive quality attributes (A), one-dimensional quality attributes (O), must-be quality attributes (M), indifferent quality attributes (I), and reverse quality attributes (R). A [PERSON] questionnaire allows for determining individual features/requirements of customers and referring to the significance of quality-perception features [32]. [PERSON]'s questionnaire is designed to ask questions about customer needs, and each question on customer needs is answered in a functional and dysfunctional format [29; 33]. The classification of attributes can be obtained by cross-checking the results of the positive and negative responses of the interviewees. Participants can choose from five response options when answering each item: \"I like it that way\", \"I expect it to be that way\", \"I am neutral\", \"I can accept it that way\", and \"I dislike it that way\". Table 1 provides a questionnaire matrix that categorizes a quality attribute as either functional or dysfunctional. [PERSON] et al. [34] found that the customer's most important quality element was must-be quality followed by one-dimensional quality. Therefore, when some quality attributes cannot be classified into a certain category, the classification rule is M \(>\) O \(>\) A \(>\) I [35]. In addition, [PERSON] et al. [33] developed two customer satisfaction indices based on [PERSON]'s model to analyze the impact of meeting certain attributes on customer satisfaction. The satisfaction increment index (SII) is used to measure the increase in customer satisfaction after a certain attribute is met, while the dissatisfaction decrement index (DDI) is used to measure the decrease in customer dissatisfaction after meeting their demand [33; 34]. SII and DDI are calculated using the percentage numbers of the A, O, M, and I from [PERSON]'s model. The formulas used to calculate customer satisfaction coefficients are shown below [33]. \[\text{Satisfaction increment index (SII) }=\frac{\text{(A+O)}}{\text{(A+O+M+I)}} \tag{1}\]  
\[\text{Dissatisfaction decrement index (DDI) }=\frac{\text{(O+M)}}{\text{(A+O+M+I)}\times\text{(-1)}} \tag{2}\]  
[PERSON]'s model has been applied in many other industries. [PERSON] et al. [37] conducted a systematic search of databases to explore the application of [PERSON]'s model in service quality improvement, business growth, and sustainability in the healthcare industry. Moreover, [PERSON] et al. [38] employed the [PERSON] methodology in the hotel industry and obtained valuable insights that can guide hotel operators who intend to incorporate technology in their establishments.