Evaluating assumptions of scales for subjective assessment of thermal environments – do laypersons perceive them the way, we researchers believe?

Schweiker, M., Abdul-Zahra, A., André, M., Al-Atrash, F., Al-Khatri, H., Alprianti, R. R., … Zomorod , Energy and Buildings ,211 (2020)

The first part of the widely used and often cited definition of thermal comfort states that “thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation” [1]. Despite the apparent simplicity and elegance of this definition, determining and providing such conditions is a complex and partly unresolved task.

As stated in the second part of the definition, thermal comfort “is assessed by subjective evaluation” [1]. Rating scales are widely used to collect such subjective evaluations of thermal conditions in built environments. Most commonly, thermal sensation is assessed to determine whether a specific thermal condition can be considered comfortable or not [1,2]. The most prominent scale used for the assessment of thermal sensation is the ASHRAE 7-point scale, which consists of seven verbal anchors: “cold”, “cool”, “slightly cool”, “neutral”, “slightly warm”, “warm”, and “hot”. Thereby, the objective is to describe a one-dimensional relationship between the physical parameters of the indoor environment such as air temperature, mean radiant temperature, air velocity, relative humidity, personal parameters such as activity level and clothing insulation, and subjective thermal sensation [3]. At the same time, ISO 10551 [4] suggests to use one or more dimensions for the assessment of thermal perception depending on the subject of the examination. Dimensions mentioned in ISO 10551 are thermal sensation (from “cold” to “hot”), affective aspects (the level of discomfort “comfortable” to “very uncomfortable”), thermal preference (from “colder” to “warmer”), personal acceptance (“generally acceptable”, “generally unacceptable”), and tolerance of the indoor environment (5-points from “perfectly tolerable” to “intolerable”). Regarding data analysis, ISO 10551 [4] gives guidance on both the analysis of thermal sensation votes obtained on ordinal measurement level as well as the determination of percentage of dissatisfied from thermal sensation votes obtained from relatively small samples of respondents. These guidelines seem to be rarely applied in practice.

Several explicit and implicit assumptions underlie the usage of these rating scales. The following three of these assumptions relevant for rating scales applied in the area of thermal comfort research will be briefly introduced in the background section and further explored in light of the results in the discussion section. These are assumptions related to:


The distances between individual verbal anchors of a scale,


the relationship between verbal anchors from different dimensions of rating scales, and


the independence of the scale interpretation of the context in which the scale is used (climate zone, season, etc.).

This paper reports the results of a large-scale international collaborative questionnaire study, which had as its main objectives:


To review the validity of some of these assumptions related to scales for subjective assessments of thermal environments and;


to investigate possible differences in the interpretation of such scales due to the context (e.g. climate, or season).

Beyond the scope of this introduction and paper are discussions related to the type of scales (ranging from binary outcome, verbal description, multi-point scales, to visual analogue scales) or the number of anchors used (see e.g. [5], [6], [7], [8] for further discussions of this topic).

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