## 2 Materials and Methods  
### Research Design  
To study the relationship between perceived indoor environmental quality (IEQ) and its effect on social housing occupants' health-related quality of life (HQoL), a self-administered paper questionnaire was designed based on the IEQ literature and SF12v2, which is a 12-item health survey that is widely used to assess people's health-related quality of life [29]. The questionnaire comprised four parts and received ethical approval from the University of Liverpool's Ethics Committee (approval number V02050722). The design of the questionnaire was aimed at identifying the most direct correlations between IEQ and health outcomes within the specific research objectives and the characteristics of the target population. The first part of the questionnaire collected a respondent's demographic and background information, such as age, gender, employment status (Emp_stat), educational level (Edu_stat) and personal habits that may affect health, like smoking (Smo_stat) and alcohol drinking (Alc_stat) status. In the second part, respondents described how long they had lived in their residence (L_dura), floor level (H_floor), the number of thermal controls and adjustment solutions (Num_Tcontrol), overall satisfaction with temperature (OS_T), and the number of sources to cause thermal discomfort (Num_Tdis). The third part of the questionnaire asked about overall satisfaction with indoor air quality (OS_AQ) and sources of dissatisfaction, focusing on a number of issues, if any, that caused odour problems (Num_Odo). The satisfaction ratings were evaluated on a 7-point Likert scale, with the dissatisfied answers prompting follow-up questions to make the occupants evaluate their sources of dissatisfaction. Finally, the last part of the questionnaire included the SF-12v2 Health Survey (SF12), with the license agreement from QualityMetric Incorporated, measuring eight health domains in physical (PF) and social functioning (SF), bodily pain (BP), general health (GH), vitality (VT), role limitations due to physical (RP) and emotional (RE) health problems, and mental health (MH), with each domain contributing to the physical (PCS) and mental (MCS) component scores. The SF12v2 Health Survey has been widely validated for predicting a population's mental and physical health [30; 31], including low socio-economic populations [32]. To enrich an understanding of the factors influencing indoor air quality and thermal comfort satisfaction, this study focused on variables directly related to the resident's immediate living environment and perceptions of their health. This focus was in response to a strategic decision to prioritise the investigation of tangible and perceivable aspects of IEQ that residents could reliably report. While recognising the potential influence of broader socio-economic factors, such as household income and housing maintenance status, on perceptions of air quality, this study opted to focus its analysis on variables that offered the most direct insight into the relationship between IEQ and health outcomes within the specific context of the Zerdely social housing district. The research design is shown in Figure 1. The independent variables consist of perceived thermal and air qualities of the indoor climate satisfaction levels and actions taken to alter their interior environment. The covariates were included in terms of two dimensions: housing and living and demographic and socio-economic conditions. The apartment's floor level (H_floor) and the length of occupation (L_dura) were considered under the housing and living conditions, and the essential details about the residents and their behaviours were considered under demographic and socio-economic characteristics. The primary dependent variable was the residents' self-rated physical (PCS) and mental (MCS) health components, as well as overall satisfaction with thermal (OS_T) and air quality (OS_AQ).