## 3 Methodology
### Service and Network Quality Efficiency Model  
The research model, including the four DEA models tested in this study, is visualized in Figure 1, while the details of the four DEA models are given in Table 1. The four DEA models are conducted to analyze management efficiency, service quality efficiency, network quality efficiency, and market efficiency using the following input and output factors. First, Model 1 measuring management efficiency assigns total asset (fixed cost) and operating expense (variable cost) as input factors and operating income and total revenue as output factors. Model 2 for service quality efficiency and Model 3 for network quality efficiency also use the same input factors as Model 1, while for output factors, Model 2 uses customer care and purchase experience and Model 3, download speed and upload speed. The values for customer care and purchase experience were extracted from indices provided in J.D. Power's \"U.S. Wireless Customer Care Full-Service Performance Study\" and \"U.S. Full-Service Wireless Purchase Experience Study\", and the data for average download and upload speed from a survey conducted by NOVARUM for the U.S. region.  
Lastly, Model 4 uses the efficiency scores for service quality and network quality gained from Models 2 and 3 as input factors with operating income and total revenue, the output factors for Model 1, as output factors to analyze market efficiency, which shows how effectively revenue is gained through service and network quality efficiency. In other words, these factors measure how well the firm utilizes its efficiency in service and network quality to maximize revenue in the market, which translates to market efficiency.  
After the management efficiency, service quality efficiency, network quality efficiency, and market efficiency scores gained from performing DEA for Models 1-4 are tested using Mann-Whitney U test to verify the similarity in efficiency among the DMUs. The Mann-Whitney U test is used as the verification method, rather than the generally-used \(t\)-test, because DEA is a nonparametric statistics analysis method. As the main purpose of this study is to identify which between service quality and network quality efficiencies determine management efficiency, this study tests three hypotheses as follows:  
* H1: The distribution of management efficiency and service quality efficiency are the same across.
* H2: The distribution of management efficiency and network quality efficiency are the same across.
* H3: The distribution of management efficiency and market efficiency are the same across.  
To visualize the relationship between network quality efficiency and service quality efficiency in DMUs, a 2 by 2 matrix is used to plot the DMUs based on their efficiency scores. The matrix is presented in Figure 2 below. In this matrix, Quadrant A shows efficiency in terms of establishing service quality while Quadrant B indicate efficiency in both service quality and network quality. Quadrant C represents inefficiency in both aspects. Lastly, Quadrant D denotes inefficiency in terms of establishing network quality.  
Figure 2: Relationship between network and service quality efficiency.