The Social Housing Outcomes Worth Study aims to find out how housing conditions, particularly crowding, affects health and well-being.

Quick Links

Major Publications Include

Health Impacts of Social Housing: Hospitalisations in Housing New Zealand Applicants and Tenants, 2003-2008 (63pp)
Michael Baker, Jane Zhang, Philippa Howden-Chapman

Health Status of Housing New Zealand Applicants & Tenants 2004-2008 (112pp)
Michael Baker, Jane Zhang, Philippa Howden-Chapman

Housing, Crowding and Health Study: Characteristics of cohort members and their Hospitalisations -February 2003 to June 2005 (Interim Report, 26 July 2006) (PDF).
Michael Baker, Jane Zhang, Philippa Howden-Chapman, Tony Blakely, Kay Saville-Smith, Julian Crane.

Information for participants

The Housing, Crowding and Health Study is a nationwide study which ran for five years and involved all Housing New Zealand Corporation (HNZC) tenants and applicants.

The study aimed to find out how housing affected the health and well-being of tenants with the hope that participation in the research could lead to better, healthier housing for New Zealanders.

What was involved?

  • a Main Study, which included all HNZC tenants and applicants; and
  • a Household Survey, which involved only a small number of HNZC tenants and applicants

Main Study

Information you give HNZC when you apply for a house or income-related rent will be given to the New Zealand Health Information Service, and matched with any overnight hospital visits. Your name and contact details will be removed from the information, and some of the data will be given to the University of Otago, Wellington.

You will also be asked questions by HNZC about smoking cigarettes. It is a yes/no answer. It is your choice whether you answer these questions. The answers you give will not affect your rent or application for housing. The answers will be given to the University of Otago, Wellington researchers. They will not be used by HNZC.

You do not need to answer the question about your smoking, but it would be helpful if you did.

Household Survey

HNZC will ask you if you want researchers to call you about the household survey. You will find a tick box at the end of the Privacy Statement on an Income-related rent form or a Needs assessment form (application for housing).

If you would like to find out more about the Household survey to decide whether or not to take part in it, tick the box in the Privacy Statement that HNZC will give you.

If you tick the box, you may be contacted sometime during the five-year study to ask if you would like to be interviewed in more detail about your housing and health. Not everyone who ticks the box will be contacted.

If you do take part in an interview, your answers will be kept completely confidential by the research team, and will not be passed onto any other people or agency.

Information for those with an interest in science and policy implications

Background to the Housing, Crowding and Health Cohort Study

The impetus for this study initially came from the fact that New Zealand is experiencing high rates of severe infectious diseases, notably a prolonged meningococcal disease epidemic (Baker, Martin et al. 1999), increasing rates of locally acquired tuberculosis (Kieft, Perks et al. 2000), and sustained high rates of rheumatic fever (Baker and Chakraborty 1996), childhood pneumonia (Grant 1999), and cellulitis (serious skin infections). A large case-control study of meningococcal disease in Auckland children showed that household crowding was the most important risk factor for this disease (Baker, McNicholas et al. 2000).

The link between overcrowded housing and infectious diseases has long been assumed, but the number of rigorous investigations of this link is still small. It is logical that household overcrowding increases transmission of infectious diseases, particularly those spread by respiratory means and direct person-to-person contact. Given that overcrowding increases contact between people, it is highly plausible that overcrowding is also associated with higher rates of skin and enteric (intestinal) diseases (Patel, Mendal et al. 1994; Staat, Kruszon-Moran et al. 1996; Pavia, Nielsen et al. 1990; Redlinger, O'Rourke et al. 1997; McCallion, Murray et al. 1996).

The relationship between overcrowding and health is complex. Overcrowding is associated with other health determinants such as income as well as exposure to other risk factors such as tobacco smoke. Some studies found that people who live in more crowded housing have poorer physical and mental health (Ministry of Health 1999; Howden-Chapman and Wilson 2000) .

There is little research on the health effects of improvements to housing. Two studies showed that people with pre-existing health condition, when rehoused with improved living conditions into state-subsidised rental housing, used health services less than before (Smith 1999; Kearns, Smith et al. 1992). A recent review in the British Medical Journal found no published studies on the effects of reductions in household crowding on the risk of infectious diseases (Thomson, Petticrew et al. 2001).

The Housing, Crowding and Health cohort study is a joint research project between the University of Otago, Wellington and the Housing New Zealand Corporation (HNZC). The study will utilise the fact that the largest provider of public housing in New Zealand, HNZC, obtains and stores detailed records on all applicants and existing tenants. These processes allow for collection of information on exposure to housing conditions in a large cohort of households. The HNZC collects information on household crowding and other housing conditions, and important socio-demographic data like the age, sex and income details of their customers. This information has been regularly collected via two separate processes – a Needs assessment semi-structured interview and a self-completed Income-related rent application. These processes also allow for collection of additional information on important confounding factors, notably ethnicity, and tobacco smoke exposure. This research will use, as the measure of health outcomes, hospitalisations for infectious diseases and other conditions as recorded by the New Zealand Health Information Service. Using hospitalisations has the advantage that it is inexpensive, logistically easy to use, and is relatively complete for serious infectious diseases such as meningococcal disease.

The Housing, Crowding and Health study has been designed as a cohort study. Because it can measure multiple health outcomes, the cohort study provides potentially the most efficient way of investigating and attempting to quantify the overall burden of disease that can be attributed to household crowding.


  • Baker M, Chakraborty M. (1996). Rheumatic fever in New Zealand in the 1990s: still cause for concern. N Z Public Health Rep 3(3): 17-9.
  • Baker M, Martin D, Kieft C et al. (1999). The evolving meningococcal disease epidemic in New Zealand. N Z Public Health Rep 6(8): 57-61.
  • Baker M, McNicholas A, et al. (2000). Houshold crowding a major risk factor for epidemic meningococcal disease in Auckland children. Pediatr Infect Dis J. 19(10): 983-90.
  • Grant CC. (1999). Pneumonia in children: becoming harder to ignore. NZ Med J 112(1095): 345-7.
  • Howden-Chapman P, Wilson N. (2000). Housing and Health. In: Howden-Chapman P, Tobias M. Social inequalities in health: New Zealand 1999. Wellington: Ministry of Health. p 133-46.
  • Kearns RA, Smith CJ et al. (1992). The stress of incipient homelessness. Housing Stud 7(4): 280-98.
  • Kieft, Perks M, Baker M, et al. (2000). Annual surveillance summary 1999. Wellington: Institute of Environmental Science & Research.
  • McCallion WA, Murray LJ, Bailie AG, et al. (1996). Helicobacter pylori infection in children: relation with current household living conditions. Gut 39(1): 18-21.
  • Ministry of Health. (1999). Taking the pulse: the 1996/97 New Zealand health survey. Wellington: Ministry of Health.
  • Patel P, Mendall MA, Khulusi S, et al. (1994). Helicobacter pylori infection in childhood: risk factors and effect on growth. BMJ 309(6962): 1119-23.
  • Pavia AT, Nielsen L, Armington L, et al. (1990). A community-wide outbreak of hepatitis A in a religious community: impact of mass administration of immune globulin. AM J Epidemiol 131(6): 1085-93.
  • Redlinger T, O'Rourke K, VanDerslice J. (1997). Hepatitis A among schoolchildren in a US_Mexico border community. Am J Public Health 87(10): 1715-7.
  • Smith SJ. (1999). Housing for health in the 21st century. Conference paper. Annual Conference of the New Zealand Public Health Association, Wellington
  • Staat MA, Kruszon-Moran D, McQuillan GM, et al. (1996). A population-based serologic survey of Helicobacter pylori infection in children and adolescents in the United States. J Infect Dis 174(5): 1120-3.
  • Thomson H, Petticrew M, Morrison D. (2001). Health effects of housing improvement: systematic review of intervention studies. BMJ 323: 187-90.

Study Questions

  1. Do people living in more crowded households have higher rates of hospitalisation for infectious diseases, after controlling for age, ethnicity, socio-economic factors and tobacco smoke exposure?
  2. Are reductions in household crowding, as achieved when people are placed in a Housing New Zealand Corporation (NNZC) house, associated with a reduction in hospitalisations for infectious diseases?
  3. Does tobacco smoke exposure interact with crowding to increase hospitalisations for respiratory infectious diseases?

Frequently Asked Questions

Why is this study important?

Results of this study will be used to help communities that are at greater risk of housing-related health problems. The study outcomes will give researchers a better understanding of how crowded housing affects people's health and well-being. These results can be used to assess the burden of serious infectious disease in New Zealand that could be prevented by efforts to reduce household crowding. They may also be used to identify better ways of designing housing in New Zealand. The results of this study could make an important input into housing policy decisions in New Zealand and internationally.

Why should I take part in this study?

Although you, personally, will not benefit from participating in the study, this study will help communities that are at greater risk of housing-related health problems. Through your participation, health researchers and housing providers will better understand how crowded housing affects people's health and well-being.

Why do we ask about smoking?

Our researchers need to be sure that the illnesses they are studying are due to crowded housing and not due to cigarette smoking. Smoking cigarettes is associated with some of the diseases we are researching and we need to know about smoking in your household to separate the effect of smoking cigarettes from the effect of crowding on disease rate.

What happens if I change my mind about being involved in the Household Survey?

You can pull out of the Household Survey at any time by contacting the University of Otago, Wellington on 0508 478 839.

How will this study help improve the health of New Zealanders?

The research will provide information to support housing policies and practices that will help improve the health of people in New Zealand and internationally.

In terms of Maori and Pacific people, research shows they are disproportionately affected by diseases linked to overcrowding, and research is required to help reduce the risk of illness within this population. As 50% of HNZC tenants are Maori and Pacific people, a large group of the population has potential to benefit from any changes to housing policy.

Are there any side effects for participants in the study?

There are no risks or side effects for participant in this study. HNZC has worked to ensure that the privacy of tenants and applicants is protected and the study has been approved by the Wellington Ethics Committee on behalf of all New Zealand ethics committees. Information provided to the University of Otago, Wellington will not identify individuals unless they agree. Information gathered by the University of Otago, Wellington research team will not be passed on to HNZC, and will not affect rent, tenure or housing application. The study results will not include any names, and will be published only as group findings.

How does your housing affect your or your family's health?

The Housing and Health Research Programme – He Kainga Oranga – has been set up to answer the above question. There is evidence that cold, damp, mouldy and overcrowded houses are bad for health. These conditions may make asthma and some other lung diseases worse. The studies which are part of this programme are particularly aiming at investigating how housing improvements, such as house insulation, can improve health. The initiative to study crowding came from results of the meningococcal disease risk factor study of Auckland children published in 2000. The study showed that the risk for a child developing meningococcal disease was strongly linked to household crowding. The risk of infection becomes greater with each additional member of a household.

The Housing, Crowding and Health study extends this previous research by looking into the links between crowding and all infectious diseases. It also aims to see if moving from a more crowded to a less crowded house reduces this risk of disease.

What is a cohort study?

A cohort study is an epidemiological study in which a group of people is followed for a period of time. The researcher collects information about exposure to different factors or specific agents, and the disease occurrence in people who were exposed to the factor(s) of interest is compared with those who were not exposed. As diseases occur rarely, a large number of people must be followed up for a long period of time. Because they are robust and internally valid, cohort studies provide the most convincing evidence of links between exposure to specific factors and disease.

Study investigators and how to contact them

The research team includes medical doctors, scientists and other health professionals.

Principal Investigator:

Dr. Michael Baker


Professor Philippa Howden-Chapman
Professor Julian Crane
Professor Tony Blakely
Dr Sunny Collings

Data Manager/Analyst

Jane Zhang

For further information about the study you can call the University of Otago, Wellington research team on freephone 0508 478 836 Monday – Friday 9am – 5pm.

If you are a HNZC tenant and are concerned you may be living in a crowded environment, please talk with your Tenancy Manager.