## 3 Results
### Question 3: Which Aspects and Indicators Should IEQ Models Include?  
#### 3.3.1. IEQ Aspects Involved in the Existing IEQ Models  
Most existing IEQ models considered the four main aspects of IEQ-IAQ: thermal quality, visual quality, and acoustic quality [1; 5; 8; 10; 13; 14; 15; 17; 42; 48; 49; 50; 51; 52; 53; 54; 55]. Among the other models that did not involve all four IEQ aspects, thermal comfort was the most widely investigated; all the reviewed models considered it, but while IAQ was not included in the models developed by [PERSON] et al. [56], [PERSON] et al. [57], and [PERSON] et al. [58], visual quality was not included in the models proposed by [PERSON] and [PERSON] [41], [PERSON] and [PERSON] [59], and [PERSON] and [PERSON] [60], and acoustic quality was not included in the models provided by [PERSON] et al. [58] and [PERSON] and [PERSON] [59]. The reason why these aspects were excluded differed between the studies, which might be due to the narrow range of the collected data [57; 60], the research purposes [59], or the limitations of the experiment chamber [58]. However, according to [PERSON] et al. [61], there were significant interactions between the four IEQ aspects; for example, they found that under the same IAQ conditions, the occupants' assessments of smells were different with different lighting or acoustic quality. This sensory interaction might influence the occupants' overall IEQ assessment as well. Therefore, to achieve accurate IEQ perception, the four aspects should be considered simultaneously.  
Although IAQ, thermal comfort, visual quality, and acoustic quality have been regarded as significant components of IEQ, the subject encompasses more conditions inside the building. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) defined IEQ as \"a perceived indoor experience of the indoor building environment that includes aspects of design, analysis, and operation of energy-efficient, healthy, and comfortable buildings\" [62]. Therefore, the Center for the Built Environment (CBE) at the University of California, Berkeley, designed a web-based IEQ assessment questionnaire that consists of an evaluation of seven indoor environmental quality aspects, including office layout, office furnishings, thermal comfort, air quality, lighting, acoustics, and cleaning/maintenance [63]. Many researchers later applied this questionnaire to evaluate IEQ in several investigated buildings [40; 64; 65]. They found that apart from the four widely studied IEQ aspects, office layout, furnishing, and cleanliness (including indicators such as the amount of space, privacy, and the adjustability of furniture) had noticeable impacts on the occupants' overall satisfaction [21; 40; 66]. Therefore, these aspects of IEQ are suggested for consideration in developing IEQ models. Electromagnetic fields, water quality, and energy were investigated in some IEQ assessments, due to society's goals at the time and the severity of the problems that these aspects might cause [67; 68; 69]. However, no IEQ model has involved these aspects so far.  
Since IAQ, thermal comfort, visual quality, and acoustic quality were the most widely studied factors, they are the main focus of the current study. In most previous studies, only one indicator was selected to represent one aspect of the IEQ, such as predicted mean vote (PMV)/operative temperature (Top) for thermal comfort, CO\({}_{2}\) concentration for IAQ, illuminance for visual quality, and sound pressure level (SPL) for acoustic quality [13; 14; 42; 50; 60]. However, more parameters could affect these aspects of IEQ. Hence, to achieve a holistic understanding of IEQ performance, some studies have investigated more than one indicator for some or each IEQ aspect(s) [48; 51; 55; 56]. A few researchers even included 18 [64] or 23 [69] indicators in their own IEQ evaluation surveys. The most commonly used indicators for each IEQ aspect will be discussed in the following sub-sections.