Nonlinear relationships between individual IEQ factors and overall workspace satisfaction
Highlights
► Kano’s satisfaction model is applied to the CBE database of occupant satisfaction. ► Different IEQ factors have different types of influence on occupant satisfaction. ► IEQ factors are classified as Basic, Bonus and Proportional Factors.
Introduction
The topic of Indoor Environmental Quality (IEQ) seems to be generating increased research activity in response to growing awareness of the significance of IEQ issues to office-based workforces, and the linkage of sick building syndrome to poor IAQ (e.g. [1], [2], [3]) has served to heighten this awareness. Apart from health issues, some researchers justify indoor environment research by noting that human resources account for the largest proportion of total expenses in the life cycle of a building (e.g. [4], [5]). Occupants who are satisfied with the overall environmental quality of their workspace are widely assumed to be more productive (e.g. [6], [7]). In addition, it seems that occupants are being regarded like consumers of the product (building) and as such, entitled to be satisfied with the indoor environmental product. Consequently, more research works dealing with building occupant satisfaction are being conducted than ever before. Finally, the adoption of occupant satisfaction surveys in the IEQ section of building sustainability rating schemes such as LEED (Leadership in Energy and Environmental Design) [8] and NABERS (National Australian Built Environment Rating System) [9] has sharpened the focus on how occupants perceive and use buildings.
A number of studies have attempted to understand the quantitative relationship between occupant overall satisfaction and the building’s performance on individual IEQ factors such as thermal comfort, acoustic quality, air quality and visual comfort, primarily to find out which has the most significant effect on occupant satisfaction. Based on a comprehensive literature review, Frontczak and Wargocki [10] report that thermal comfort is slightly more important than other IEQ factors. However Fig. 1 indicates that this finding was not universally consistent across all research papers on this question [10]. Some researchers remain sceptical because myriad confounding factors can potentially distort the relationships between occupant satisfaction and IEQ factors [6], [11]. It is becoming clear that increases in occupants’ overall satisfaction do not correspond uniformly to improvements of individual IEQ factors [12], [13]. Some researchers argue that studies into occupant satisfaction need to take account of wider, contextual factors such as personal, situational and social factors, each of which may affect occupants’ overall satisfaction with their building [11], [14]. Nevertheless there has been no previous research on the nature of the relationship itself: how does occupant overall satisfaction correspond to the building’s performance on individual IEQ factors?
The question of defining the functional dependence of overall satisfaction upon a variety of individual properties is a generic one that can be found in many different disciplines. Marketing literature is replete with studies dealing with customer satisfaction and how it is influenced by specific properties or qualities of the product or service in question [15], [16], [17], [18]. Kano [15] developed a model of customer satisfaction based on a classification of the type of relationship between specific product qualities and overall satisfaction. Different qualities or factors impact overall customer satisfaction in different ways: some in a positive way, some in a negative way, and some in both directions. The present study enquires whether Kano’s customer satisfaction model is applicable in the context of building occupants and indoor environmental qualities, with a view to better understanding the relationship between overall satisfaction and the perceived performance on specific IEQ factors. The aim of this analysis is to prioritize various IEQ factors in a way that enhances the effectiveness of building management.
The structure of this paper is as follows: First, Kano’s model of satisfaction is briefly described. Second, using a large Post Occupancy Evaluation (POE) database [19] an empirical test is performed on this hypothesis: different IEQ factors affect occupants’ overall satisfaction in different ways: some linear and some nonlinear. Third, through statistical analysis, occupant overall satisfaction is estimated and the IEQ factors are categorized with Kano’s model. Finally, the implication of the study outcome for building management is discussed.
Section snippets
Kano’s model of satisfaction
In the discipline of marketing research, the relationship between customer satisfaction and the quality of a product or service has usually been assumed to be one-dimensional [20], [21], i.e. the level of customer satisfaction is linearly dependent upon product quality; the higher the quality, the more the customers will be satisfied. However, when it comes to ‘satisfaction’, it does not always work as anticipated. In most instances, the relationship between the performance of a product and
Occupant survey sample: CBE’s database
The occupants’ survey database from CBE (Center for the Built Environment) at the University of California, Berkeley is used for the empirical test. CBE has conducted occupants’ survey since 2000 [26] and cumulated data from more than 600 buildings with various usages as of June 2010 [27]. It is a web-based survey tool covering various IEQ dimensions such as thermal comfort, air quality, lighting, acoustic quality, office layout, office furnishings, and cleanliness & maintenance [19]. Occupants
Results
First of all, the assumption of data normality was confirmed by histogram and normal probability plot. Also, the database used for these multiple regression analyses was internally consistent, or reliable (Cronbach’s Alpha = 0.89). The proportion of variance in overall satisfaction explained by the multiple regression model was 63% (R2 = 0.63), so the resultant model provided useable predictive capability for occupants’ overall satisfaction. Finally, the degree of multi-collinearity of an
Applicability of Kano’s model into IEQ domain
The first research question of this paper can now be addressed; “Can Kano’s model of customer satisfaction be generalized to the IEQ domain?” The results of this analysis of the CBE Post Occupancy Evaluation (POE) database indicate that Kano’s model generalizes successfully to the IEQ domain. Although no Bonus Factors were identified, some IEQ factors had a predominantly negative impact (Basic Factors) while the others had a linear relationship with overall satisfaction (Proportional Factors
Conclusions
By analyzing CBE’s occupant survey database, this study identified the nonlinear relationship between IEQ factors and occupant overall satisfaction. And by employing Kano’s model, IEQ factors are categorized into Basic Factors and Proportional Factors according to their influence on occupant satisfaction.
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First, ‘temperature’, ‘noise level’, ‘amount of space’, ‘visual privacy’, ‘adjustability of furniture’, ‘colours & textures’ and ‘workspace cleanliness’ were classified as Basic Factors. Their
Acknowledgement
The authors thank the Center for the Built Environment at the University of California, Berkeley, for generously permitting our access to the CBE occupant survey database for this analysis. Particularly the authors would also like to thank Monika Frontczak from ICIEE at Technical University of Denmark, for her invaluable efforts in organizing and formatting the database. This study was partially supported by the Jean and Andrew Wong Research Scholarship at the University of Sydney’s Faculty of
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