Elevated physiological symptoms related to

air-conditioning use while sleeping: a longitudinal

cohort study in NUS

Research proposal

Ying Chen, Xiaohe Li, Divya Balasubramanian

Saw Swee Hock School of Public Health

National University of Singapore

A0078002, A0123847, A0120163

April 15, 2015

i

Abstract

Background

Cross-sectional studies have consistently shown that health problems are related to air-conditioning

use in tropical regions. We intend to conduct our study with students in the residences of Na-

tional University of Singapore. We are interested in the night exposure to air-conditioning as

CO2 levels are found to be higher in air-conditioned rooms and suspected to cause elevated

physiologic symptoms. We hypothesize that exposure to air-conditioning during sleep is a risk

factor for health conditions in terms of respiratory systems and central nervous systems, skin

problems. We also hypothesize there could be a dose-response relationship between the inten-

sity and temperature of the exposure and health conditions.

Method

A longitudinal cohort study will be conducted in two cohorts of residents from National Uni-

versity School. Participants will be followed up for a semester where exposure, potential

confounders, and outcomes will be measured repeatedly. Logistic regression and poisson re-

gression will both be used for analysis. To account for the time correlation between outcomes

from the same subject and adjust for time-varying covariates, generalized linear mixed model

will be applied.

ii

Contents

1 Introduction 1

2 Problem Statement 2

2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.2 Research Question/Hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3 Objectives and Aims 3

3.1 Overall Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.2 Specific Aims . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4 Background and Significance 4

5 Research Design and Methods 5

5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

5.2 Population and Study Sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

5.3 Inclusion and Exclusion Criterion . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5.4 Sample Size and Selection of Sample . . . . . . . . . . . . . . . . . . . . . . . . 6

5.5 Sources of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5.6 Collection of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.7 Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.8 Outcome Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5.9 Missing Data Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5.10 Data Analysis Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5.11 Ethics and Human Subjects Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.12 Timeframes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

6 Strength and Weakness of the Study 10

6.1 Strengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

iii

6.2 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6.2.1 Selection bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6.2.2 Information bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6.2.3 Reverse causality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6.2.4 Generalizability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6.3 Public Health Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Appendices 14

iv

1 Introduction

Lifestyle of the urban population has been changing radically in the last two decades. The invasion

of air-conditioners has made air-conditioning almost inescapable in our daily life. Particularly in

Singapore, air-conditioning can be everywhere when we are going out by buses, trains, visiting

clinics, having classes in the university, staying within stations, shopping at malls, working at

offices and so on. Most of our day time are spent in an air-conditioned environment. Interestingly,

health problems and discomforts, referred to as sick building syndrome or tight building syndrome,

has been recognized to be related to the quality of indoor air along the changes for over fifteen

years [1].

Problems associated with indoor air quality is considered to be a common environmental health

issue faced by clinicians, because the factors associated with the perceived indoor air quality or

indoor air problems are not fully understood. It can be said with certainty that no known toxins are

found to be causing these symptoms. And there have not been any standardized tests or instruments

used to define this as a syndrome [2]. This has made it all the more difficult to clearly identify the

associations and the causal inference from the associations.

There are studies that have compared the indoor air quality while sleeping in the air-conditioned

and the naturally ventilated buildings. The results from such studies suggest an association between

the air-conditioner use and the symptoms of the respiratory or central nervous systems. The sug-

gested causal relationship is that the air-conditioning leads to an increased carbon dioxide levels

inside the room due to changes in humidity, temperature and ventilation rates and this could in

turn lead to discomfort or even health problems [3]. The most important factors that have been

attributed to affect indoor air quality is the presence of heating, ventilation and air-conditioning

systems. There are analyses that showed an increase in the mentioned symptoms of about 30% to

200% in air-conditioned buildings compared to natural ventilation [5].

A weakness identified in such studies are the difficulties in finding a perfect control group

where there is absolutely no exposure to air-conditioning given surroundings are almost always

air-conditioned. The other difficulties include controlling for potential confounders that might

1

bias the conclusions. In view of all these, we are motivated to restrict our study to a relatively

homogenous population and examine the effect of air-conditioning only during sleep on health

problems.

2 Problem Statement

2.1 Overview

In Singapore, the usage of air-conditioners have been changed significantly in the last decade due

to the huge economic development. The hot, humid and wet climates have led to increasing us-

age of air-conditioners in this fast developed island. Singapore is one of the tropical countries

where air-conditioning is of great concern because one study in energy consumption done in Na-

tional University of Singapore have reported that heating, ventilation and air-conditioning have

contributed up to 50% of the total energy consumption in whole Singapore [4]. Studies have

shown that there is potential association between respiratory systems related symptoms and other

sick building syndromes and exposure to air-conditioning. Step-down in performance of people

could be related to environmental conditions that cause an increase or decrease in the body core

temperature [5]. However there are only a few studies conducted in this area and we need more

studies to confirm if there could be a causal relationship between exposure to air-conditioning and

related health problems. As described in introduction, our proposed cohort study has the advan-

tages that we could control for potential confounders by concentrating on a relatively homogenous

population and have a better control group with absolutely no exposure to air-conditioning by

studying the effect of exposure to air-conditioning during sleep.

2.2 Research Question/Hypothesis

1. Is usage of air-conditioners while sleeping associated with elevated levels of symptoms of

the upper and lower respiratory symptoms, central nervous system and skin?

2

2. Is temperature, or the duration of use of air-conditioner while sleeping associated with any

of the above-mentioned symptoms?

3. Is there a dose-response relationship of the temperature and duration with the severity of the

symptoms?

3 Objectives and Aims

3.1 Overall Objective

We will conduct a longitudinal cohort study with one group consisting of users of air-conditioner

while sleeping (exposed) and the other group consisting of non-users of air-conditioners while

sleeping (non-exposed) among the residents of National University of Singapore by following

them up for a period of four months/ one semester.

3.2 Specific Aims

1. To investigate the relationship between the exposure (temperature and duration) of air-conditioner

use and the transient outcomes that includes

• Lower respiratory (tight chest, difficulty breathing, shortness of breath, wheeze and

flu-like symptoms)

• Upper respiratory/ mucous membrane (nose, throat and eye symptoms)

• Central nervous symptoms (head ache and lethargy)

• Skin (dry skin, itching skin and skin rash)

2. To identify the specific risk factors of the transient outcomes, including temperature of air-

conditioning setting, duration of air-conditioning setting.

3

4 Background and Significance

A field study on the thermal comfort of Singapore subjects was conducted in 1988 and many other

studies in Jakarta and Bangkok to find the comfortable temperature for human beings. The study

has found that the comfortable temperature is around 27 �C in both naturally ventilated setting and

air-conditioned setting but that in naturally ventilated setting is slightly higher [6].Air-conditioning

systems are deemed responsible for recirculating pathogens and spreading them throughout the

room like Mould, bacteria, dust mites, other micro-organisms; endotoxins and other microbial

products.

Reduced ventilation rates have been found inadequate to maintain the health and comfort of

residence occupants. Heating, ventilation and air-conditioning systems (HVAC systems) also have

been found to increase the indoor air pollution. In order to have an acceptable indoor air quality

(IAQ) with a minimum energy consumption, The American Society of Heating, Refrigeration

and Air-Conditioning Engineers (ASHRAE) has set ventilation standards to a minimum of 8.4 air

exchanges per 24 hours [7] [8] [9].

It becomes all the more important while sleeping because in addition to all these factors the

carbon dioxide levels are higher in an air-conditioned room and the brain signals the breathing

muscles to breathe faster in order to expire more carbon dioxide and inspire more oxygen. If

this regulatory mechanism is disrupted and the brain’s recognition of, or response to, oxygen and

carbon dioxide levels is impaired and sleep might be disturbed [9]. Thus the temperature and

intensity of air-conditioning use, leads in turn to change in temperature, humidity and carbon

dioxide levels and microbe concentration in the room while sleeping and these factors could be the

causal factors for the elevated symptoms that have been identified.

4

Figure 1: diagram of relations

5 Research Design and Methods

5.1 Overview

Due to the short term occurring and recurring nature of symptoms of interest, we propose to do a

cohort study on residents in one of the local university in Singapore. Exposure to air-conditioning

use in sleep and symptoms of interest will be measured repeatedly four times in a monthly interval

between collection of measures

5.2 Population and Study Sample

Our study population is NUS residents, which is expected to be homogenous in terms of age (on an

average), environmental exposures, day-time exposure to air-conditioning (again on average) and

the food from the canteens (although their choices are different). We are going to use two cohorts

of residents one from the Prince George?s Park residence and second cohort from University-Town

residence. There are two types of rooms in these two residences, either provided with or without

air-conditioning. By selecting from the whole population, we can have a group of residents with

exposure to air-conditioning during sleep, and another without, the non-exposed group. Given that

accommodation contracts last for only one academic year including 2 semesters, and each semester

lasts for 4 months, excluding vacation, each of the cohort participants will be followed up from the

5

beginning of move for the next 4 months, until the end of the semester.

5.3 Inclusion and Exclusion Criterion

Inclusion:

• Residents in Utown and PGP residents.

• Stay at their current accommodation through out the study period.

Exclusion:

• Residents who sleep at their room less than 80% of time.

• Residents with long term symptoms related to our outcome of interest.

• Residents who are below 18 years old.

Due to the short term nature of our symptoms of interest and the recurrences, participants who

already have symptoms will still be at risk immediately after they recover. In view of that, we will

still include participants with short term symptoms of interest.

5.4 Sample Size and Selection of Sample

To obtain an odds ratio of 2 in effect among groups with different exposures to air-conditioning,

we estimated the sample size for the non-exposed group to be 505 and for the exposed group to

be 101, if we assume the prevalence of symptoms in exposed group to be 0.40 and the prevalence

of symptoms in non-exposed group to be 0.25 and the sample size ratio be 1:5 between exposed

group and non-exposed group which is based on the literature review [1]. This estimated sample

sizes will give us at least 80% power and around we are able to control our type-I error rate at 0.05.

5.5 Sources of Data

Office of hostel services (OHS) of the National University of Singapore

6

5.6 Collection of Data

Data will be collected through questionnaires. To recruit participants into our study, questionnaire0

will be distributed where questions will be asked regarding stay time in residence, and conditions of

long term diseases including an injury, operation affecting chest, heart problems, bronchitis, pneu-

monia, pleurisy, asthma, other chest problems and hay fever.Once ineligible students are elim-

inated from the pool,, participants will be reached to distribute questionnaire1 to obtain basic

demographics, history of accommodation types (mainly whether exposed to air-conditioning use

in sleep), history of diseases, as well as history of symptoms of interest. At the end of each month,

a follow-up questionnaire2 will be distributed regarding the exposure to air-conditioning in sleep

over the past month. Information on potential confounders like day-time use of air-conditioning,

average sleeping time per night, type of air-conditioners using will be collected as well. Having

symptoms of interest and frequency of getting these symptoms will also be asked in this follow-up

questionnaire. The participants will be called and reminded of participating in the survey. The sec-

ond questionnaire is to gather data about the exposure and the outcome of that month. Participants

who do not respond will be called and enquired about the reasons for loss-to-follow up.

5.7 Exposure Assessment

When collecting exposure information, questions regarding the frequency of air-conditioning use

during sleep(number of days per week sleep with air-conditioning on), the duration of air-conditioning

use during sleep(number of hours per night sleep with air-conditioning on), the temperature setting

about air-conditioning during sleep will be asked. Apart from the exposure information, informa-

tion on potential confounders will be collected as well. Day-time exposure to air-conditioning is a

main confounder in the relationship because day-time exposure may be related to both the expo-

sure and outcome. Another important confounder is the sleeping time, because people who sleep

for very few hours might have used air-conditioning for the same duration compared to people

who sleep for very long time. But the effect of air-conditioning could be very different for them.

The third confounder could be the type of air-conditioner because different types of air-conditioner

7

might have different effects. The other confounders include smoking, which could be a cause for

some of the respiratory symptoms.

5.8 Outcome Assessment

Symptoms of interest will be categorized into four groups: symptoms related to lower respiratory

systems (tight chest, difficulty in breathing, shortness of breath, wheeze, and flu-like symptoms);

symptoms related to upper respiratory/mucus membrane (nose, throat, and eye symptoms); symp-

toms related to central nervous systems (headache and lethargy); and symptoms related to skin

(dry skin, itching skin, and skin rash). The four categorized symptoms will be asked in a standard

questionnaire format, due to the short term occurrence and high risk of recurrences of the symp-

toms, participants who often have these symptoms will remember more clearly than those who

experience these symptoms at most only once in the one month period. The frequency of having

these symptoms asked will later be clustered to less than 2 times per month, 3-4 times per month,

and more than 4 times per month.

5.9 Missing Data Management

For participant with missing data, the answers from the previous questionnaire will be used by

assuming no changes for the recent month for that particular participant.

5.10 Data Analysis Strategies

Because our outcomes are dichotomous, logistic regression will be used to study the relationship

between exposure and each of the symptoms, as well as combination of symptoms. For the fre-

quency of outcomes, because it will be counts, poisson regression will be applied instead. In

a longitudinal study design, the correlation between repeated measurements at different timings

need to be considered and covariates might vary with time as well. To take into account of these

issues, generalized linear mixed model will be applied. Apart from specific symptoms, another set

8

of outcomes will be binary outcome of having symptoms of specific category for example, having

symptoms related to central nervous system or not. Two models will be tried out where the first

one is a simpler model where only outcome will only be modelled with exposure variables. The

second model will be more complex where potential confounders will be adjusted for the relation-

ship between air-conditioning exposure in sleep and symptoms of interest. The adjusted variables

will include age, ethnicity, gender, day-time exposure to air-conditioning, ventilation rates, air-

conditioner type and sleeping time, smoking and income. In selecting the second model, step-wise

method will be applied to select the best model.

5.11 Ethics and Human Subjects Issues

In order to conduct an ethically valid research study among the participants, the approval of the

IRB shall be obtained prior to conducting the survey. Informed consent forms shall be provided

and signed by the participants before they are given the survey forms. The data collected shall be

stored in a private PC in the university that has been secured with a password and the access to it

requires unique IDs. The data shall be stored for six years for further investigation by the ethics

committee if necessary.

5.12 Timeframes

April 2015 to April 2016

Figure 2: timeframe chart

9

6 Strength and Weakness of the Study

6.1 Strengths

By using the NUS cohort, where the population is homogenous in terms of many characteristics,

we could have avoided many unknown confounding effects. Conducting a longitudinal study and

collecting exposure and outcome measures concurrently help in providing information about onset

and dessistance, about continuity of harbouring the symptoms as well as about the within-subject

changes.

6.2 Limitations

In the study, although we made effort to adjust for potential confounders, we may still face some

risks.

6.2.1 Selection bias

Firstly, non-response bias is a serious problem. If we have a low response rate in both groups with-

out differentially distributed non-response reasons, the study will be influenced in terms of study

power. If the two groups have significantly different response rate, and the reasons of people who

do not response are related to exposures and outcome, the study would be biased. To minimize

the non-response rate, at each follow-up point, participants are called to be reminded of the par-

ticipation. Secondly, we also face the problem of loss-to-follow-up bias. During the following up

period, people may leave the study due to various reasons. Similar to the non-response bias issue,

if the lost-to-follow-up rate is very high then our sample might have a larger chance to be different

from the source population, or if the lost-to-follow-up reason is related to the outcomes of interest,

then we will have a biased conclusion. In order to minimize the lost-to-follow-up bias, reasons for

leaving the study will be enquired when participants drop out.

10

6.2.2 Information bias

In our study, information on both exposure and outcome collected through questionnaires are all

self-reported, which could have produced big risk for inaccurate information and different percep-

tions. Specifically, participants’ perception about symptoms might be very different. For instance,

participants might have different perceptions on lethargy. Another short-coming is that repeated

interviewing of the same subjects might influence their behavior.

6.2.3 Reverse causality

Symptoms resulted by air-conditioner usage will somehow influence the later on using of air-

conditioner which is the scenario of reverse causality in our study context. But under our as-

sumption that all the symptoms are short-term and they are unlikely to alter the habit of a regular

air-conditioner user, so we would say, reverse causality is not a big issue here.

6.2.4 Generalizability

Since our study will be done in NUS hostel occupants, so study subjects can not be representative

of larger population including people who are not students. We should be very considerate in

generalizing the result to larger population.

6.3 Public Health Significance

There may be several possible outcomes for our study.

One of the possibilities is that using air-conditioner during sleep is a risk factor for having

elevated symptoms. It is also possible that the association is not statistically significant. And it

may be that using air-conditioner during sleep is protective against elevated symptoms. (We think

this is not likely to be happen according to previous researches).

If we get significant results showing using air-conditioner during sleep is a risk factor, we will

come up with a suggestion regarding the proper usage of air-conditioner which at best doesn’t

11

result in elevated symptoms(e.g., no more than 30 minutes, higher than 26�C), so students in the

cohort as well as other occupants in the residences will first benefit.

Then our cohort study can serve as a pilot study in probing the association between air-

conditioner usage and risk of getting elevated symptoms in general population in Singapore.

12

References

[1] Mendell, M. J. Smith, A. H. (1990). Consistent pattern of elevated symptoms in air-conditioned

office buildings: a reanalysis of epidemiologic studies. American journal of public health,

80(10), 1193-1199.

[2] Wong, N. H., Huang, B. (2004). Comparative study of the indoor air quality of naturally ven-

tilated and air-conditioned bedrooms of residential buildings in Singapore. Building and Envi-

ronment, 39(9), 1115-1123.

[3] Mendell, M. J., Lei Gomez, Q., Mirer, A. G., Seppnen, O.,Brunner, G. (2008). Risk factors in

heating, ventilating, and air?conditioning systems for occupant symptoms in US office build-

ings: the US EPA BASE study. Indoor air, 18(4), 301-316.

[4] Yap, C., Cai, W.J., Ooi, K.T., Toh, K.C., Calavarro, G., Pillai, E.K. (2011). Air-con system

efficiency primer. National Climate Change Secretariat and National Research Foundation.

Retrieved from https://www.nccs.gov.sg/sites/nccs/files/Aircon%20Primer.pdf

[5] Okamoto-Mizuno, K., Tsuzuki, K., Mizuno, K. (2005). Effects of humid heat exposure in

later sleep segments on sleep stages and body temperature in humans. International journal of

biometeorology, 49(4), 232-237.

[6] Antic NA. Global warming and increased sleep disordered breathing mortality,rising carbon

dioxide levels are a serial pest. Respirology. 2012;17(6):885-886.

[7] Babatsikou FP. The Sick Building Syndrome (SBS). Health Science Journal.2011;5(2):72.

[8] Ruhl RA, Chang CC, Halpern GM, Gershwin ME. The Sick Building Syndrome. Journal of

Asthma. 1993;30(4):297-308.

[9] Skov P. The sick building syndrome. Annals of the New York Academy of Sciences.

1992;641(1 Sources of In):17-20.

13

[10] Wong NH, Khoo SS. Thermal comfort in classrooms in the tropics. Energy Buildings.

2003;35(4):337-351.

14

Elevated symptoms related to air-conditioner use during sleep: a cohort study in Singapore. 1

Questionnaire 0

Welcome to this study which we researchers want to look at possible associations between elevated symptomsand air-conditioning usage during sleep. Thanks for your participation!Please note that this is questionnaire number 0, which is intended to recruit participants to our study.

1. Your name:

2. Which residence do you live in? 2 PGP Residence 2 UT Residence

3. How long have you stayed in your current accommodation? years.

4. Approximately how many days in a week do you sleep in your current accommodati-on? days.

5. Have you ever had, or been told that you have had any of these disease?2 An injury, or operation a↵ecting your chest 2Heart trouble2 Bronchitis 2Pneumonia 2 Pleurisy 2 Asthma2Other chest trouble 2 Hay fever 2 Long term skin symptoms2 None

Elevated symptoms associate with air-conditioner use during sleep: a cohort study in Singapore. 1

Questionnaire 1

Welcome to this study which we researchers want to look at possible associations between elevated symptomsand air-conditioning usage during sleep. Thanks for your participation!Please note that this is questionnaire number 1, which is intended to collect basic/baseline information from

participants

About you

1. Your name:

2. Your gender: 2 Female 2 Male

3. How old are you? I am years old.

4. Which country are you from? I am from .

5. How long have you been in Singapore? years .

6. What is your ethnicity? 2 Chinese 2 Malay 2 Indian 2 Others, please specify

7. Are you a graduate student or undergraduate student? 2 graduate 2 undergraduate, whichyear? .

8. Which faculty are you from? I am from .

9. Which residence do you live in? 2 PGP Residence 2 UT ResidencePlease specify your room type .

10. How long have you stayed in your current accommodation? years.

About your general air-conditioner usage

11. Do you usually stay in places with air-conditioning during day time?2 Yes 2 No

12. Do you use air-conditioner in your previous accommodations?2 Yes 2 No

13. Do you use air-conditioner in your current accommodation?2 Yes 2 No

If No, please proceed to next section.

14. What kind of air-conditioner do you use in your current accommodation?2Residence set air-conditioner 2 Portable air-conditioner2 Others, please specify

15. Generally speaking, how frequently do you use air-conditioner in your accommodation?very often 2—2—2—2—2 very rare

16. Do you open the window when the air-conditioner is not on?2 Yes 2 No 2 Sometimes

17. Do you use air-conditioner during sleeping time in your current accommodation?2 Yes 2 No

If No, please proceed to next section.

18. On average how many days in a week do you use air-conditioner during sleep?About days.

19. On average how many hours do you keep your air-conditioner on during sleep?About hours.

20. How many degrees do you usually set for your air-conditioner during sleep?I set �C.

21. Do you use fan simultaneously with air-conditioner during sleep?2 Yes 2 No 2 Sometimes

Elevated symptoms associate with air-conditioner use during sleep: a cohort study in Singapore. 2

22. Do you open the window during sleep when the air-conditioner is on?2 Yes 2 No. 2 Sometimes

23. Do you set other functions of air-conditioner during sleep?2 No 2 Yes I set .

About smoking status

24. Do you smoke?2 Yes 2 No

If No, then

25. Have you ever smoked as much as one cigarette a day for as long as one year?2 Yes 2 No

If No to either of previous two questions, please proceed to next section.

26. How old were you when you started smoking regularly? years old.

About the conditions on elevated symptoms

0.1 Central Nervous System

27. Do you have headache?2 Yes 2 No

28. Do you get lethargy(feeling of slowness, sluggishness, tiredness, or lack of energy, and in-cluding fatigue, drowsiness, lethargy, tiredness, malaise, listlessness)?2 Yes 2 No

0.2 Upper Respiratory/Mucus Membrane

29. Do you have any of these nose symptoms?2 Blocked nose 2 Runny nose2 Others, please specify 2 None

30. Do you cough?2 Yes 2 No

31. Do you usually bring up phlegm?2 Yes 2 No

32. Do you have any of these throat symptoms?2 Dry throat 2Sore throat 2 Others, please specify2 None

33. Do you have any of these eye symptoms?2 Itching eyes 2 Irritated eyes 2 Dry eyes2 Others, please specify 2 None

0.3 Lower Respiratory

34. Do you have tight chest?2 Yes 2 No

35. Do you wheeze?2 Yes 2 No

36. Do you feel short of breath?2 Yes 2 No

37. Do you have flu-like symptoms?2 Yes 2 No

Elevated symptoms associate with air-conditioner use during sleep: a cohort study in Singapore. 3

0.4 Skin

38. Do you have any of these skin symptoms?2 Dry skin 2 Itching skin 2 Rash2 Others, please specify 2 None

Elevated symptoms related with air-conditioner use during sleep: a cohort study in Singapore. 1

Questionnaire 2

Welcome to this study which we researchers want to look at possible associations between elevated symptomsand air-conditioning usage during sleep. Thanks for your participation!Please note that this is questionnaire number 2, which is intended to collect your current elevated symptoms

condition and your air-conditioner usage during the past month

1. Your name/Participation number:

2. Approximately how many days in a week do you sleep in your current accommodati-on? days.

3. On average how many hours do you sleep everyday? hours.

4. Have you ever had, or been told that you have had any of these disease?2 An injury, or operation a↵ecting your chest 2Heart trouble2 Bronchitis 2Pneumonia 2 Pleurisy 2 Asthma2Other chest trouble 2 Hay fever 2 Long term skin symptoms2 None

About your air-conditioner usage during the past month

During the past month:

5. Do you usually stay in places with air-conditioning during day time?2 Yes 2 No

6. Have you ever used air-conditioner in your accommodation?2 Yes 2 No

If No, please proceed to next section.

7. What kind of air-conditioner do you use in your accommodation?2Residence set air-conditioner 2 Portable air-conditioner2 Others, please specify

8. Generally speaking, how frequently did you use air-conditioner in your accommodation?very often 2—2—2—2—2 very rare

9. Did you open the window when the air-conditioned is not on?2 Yes 2 No

10. Have you ever used air-conditioner during sleeping time in your accommodation?2 Yes 2 No

If No, please proceed to next section.

11. On average how many days in a week did you use air-conditioner during sleep?About days.

12. On average how many hours did you keep your air-conditioner on during sleep each day?About hours.

13. How many degrees did you usually set for your air-conditioner during sleep?I set �C.

14. Did you use fan simultaneously with air-conditioner during sleep?2 No 2 Yes 2 Sometimes

15. Did you open window when air-conditioner is on during sleep?2 No 2 Yes 2 Sometimes

16. Did you set other functions of air-conditioner during sleep?2 No 2 Yes I set .

About smoking status

17. Have you smoked over the past month?2 Yes 2 No

Elevated symptoms related with air-conditioner use during sleep: a cohort study in Singapore. 2

About the conditions on elevated symptoms

During the past month:

0.1 Central Nervous System

18. Have you ever had headache?2 Yes, time(s).2 No

19. Have you ever got lethargy(feeling of slowness, sluggishness, tiredness, or lack of energy,and including fatigue, drowsiness, lethargy, tiredness, malaise, listlessness2 Yes, time(s).2 No

0.2 Upper Respiratory/Mucus Membrane

20. Have you ever had any of these nose symptoms?2 Blocked nose, time(s).2 Runny nose, time(s).2 Others, please specify and time(s).2 None

21. Have you ever coughed?2 Yes, time(s).2 No

22. Did you usually bring up phlegm over the last month?2 Yes, time(s).2 No

23. Have you ever had any of these throat symptoms?2 Dry throat time(s).2Sore throat time(s).2 Others, please specify and time(s).2 None

24. Have you ever had any of these eye symptoms?2 Itching eyes time(s).2 Irritated eyes time(s).2 Dry eyes time(s).2 Others, please specify and time(s).2 None

0.3 Lower Respiratory

25. Have you ever had tight chest?2 Yes, time(s).2 No

26. Have you ever wheezed?2 Yes, time(s).2 No

27. Have you ever felt short of breath?2 Yes, time(s).2 No

28. Have you ever had flu-like symptoms?2 Yes, time(s).2 No

0.4 Skin

29. Have you ever had any of these skin symptoms?2 Dry skin time(s).2 Itching skin time(s).2 Rash time(s).2 Others, please specify and time(s).2 None