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Introduction to...

Longitudinal Studies


This PHCRIS Guide contains information about Australian primary health care longitudinal studies, definitions of longitudinal studies, its disadvantages and advantages, information for those wanting to conduct a longitudinal study as well as information on how to access the databases and findings of such studies.

DEFINITIONS

"Longitudinal studies provide data about the same individual at different points in time allowing the researcher to track change at the individual level.
There are a number of different types of longitudinal studies, including:

  • Individual level panel surveys, where samples of individuals are tracked and interviewed.
  • Household panel surveys, where individuals are followed within the context of the households where they live, and information is normally collected about the whole household at each wave.
  • Cohort studies, where samples from a particular age range are followed to explore their different trajectories as they age.
  • Record linkage studies, administrative or census data are linked across time."

The UK Longitudinal Studies Centre: What are longitudinal studies? - <www.iser.essex.ac.uk/ulsc/longitudinal-faqs>

"Longitudinal studies are data sources that contain observations of the same research units over a period of time. Such data can be collected either through surveys, or through linkage of administrative data."
Census.ac.uk: Longitudinal Studies - <http://census.ac.uk/guides/Longitudinal.aspx>

ADVANTAGES/DISADVANTAGES

Longitudinal studies are unique in their ability to provide useful data about individual change. This type of study also allows for flexibility, meaning the focus of the study can be shifted whilst data is being collected.

One of the biggest disadvantages to using longitudinal studies is the time factor. This type of study is time consuming, which affects cohort retention and the ability to maintain a committed research team. It also means that these types of studies are costly and the financial burden is one of the biggest challenges facing longitudinal studies. 

RESOURCES

Australian Institute of Health and Welfare (2004). Longitudinal studies of ageing: Implications for future studies, AIHW cat. no. AGE 42, 206.

Gregory A, Armstong R, Grassi T, Gaut B, Weyden M. (2008). On our selection: Australian longitudinal research studies, Medical Journal of Australia 189(11/12):650-657.

Van Weel C. (2005). Longitudinal Research and data collection in primary care, Annals of Family Medicine Vol 3(1):546-51.

Najman JM, Bor W, O'Callaghan M, Williams GM, Aird R, Shuttlewood G. (2005). Cohort profile: The Mater-University of Queensland study of pregnancy (MUSP), International Journal of Epidemiology 34:992-997.

The General Practice Research Database (GPRD)
This is the world's largest computerised database of anonymised longitudinal medical records from primary care that is linked with other healthcare data. To date, it contains data from around 5 million patients from about 625 primary care practices across the UK.

The General Practice Research Network (GPRN)
This is an Australian longitudinal database involving over 1 000 GPs who supply de-identified prescribing data for more than 3 million patients.

USING LONGITUDINAL DATA

Many studies welcome and encourage the use of their datasets as a resource for further studies.

Researchers can apply to access the data through the relevant pathways set out by the organisations that hold the data. To find out the criteria for access to specific data please view the studies' website and contact the appropriate person.

ANALYSING THE DATA

There are some great statistical software packages available that can help you analyse the data sourced from longitudinal studies. These include multi-level analysis products like MLwiN and HLM as well as some of the more generic software brands like SPSS, SAS and Stata. For more information about these software products please view the links provided.

If unsure about how to proceed with data analysis, you may find the following references useful:

Australian LONGITUDINAL STUDIES

Australian Epilepsy Research Register
National, 2006 - Ongoing

The Australian MS Longitudinal Study (AMSLS)
National, 2003 - Ongoing

Australian Longitudinal Study of Ageing
Adelaide, 1992 - Ongoing

Australian Longitudinal Study of Health and Relationships
National, 2005 - Ongoing

Canberra Longitudinal Study of the Elderly
Canberra, 1990-2002

Crossroads Undiagnosed Disease Study
Rural Victoria, 2001-2003

Diabetes and Related disorders in Urban Indigenous people in the Darwin region: The DRUID Study
Northern Territory, 2001 - Ongoing

diamond (Diagnosis, Management and Outcomes of Depression in Primary Care - a longitudinal study)
National, 2004 - Ongoing

Footprints in Time - The Longitudinal Study of Indigenous Children (LSIC)
National, 2003 - Ongoing

Growing up in Australia
National, 2003 - Ongoing

Longitudinal Surveys of Australian Youth (LSAY)
National, 1995 - Ongoing

Longitudinal study of Behavioural and Emotional Disturbance in people with Intellectual Disability
National, 1990 - Ongoing

Medicine in Australia: Balancing Employment and Life (MABEL)The Australian Longitudinal Survey of Doctors
National, 2008 - Ongoing

Participation in cervical screening by Indigenous women in the Northern Territory: a longitudinal study
Northern Territory, 1997-2004

The 45 and Up Study
New South Wales, 2008 - Ongoing

AusDiab 2005 The Australian Diabetes, Obesity and Lifestyle Study
National, 1999 - 2005, plans are now under way for a 10-year follow-up for AusDiab.

The BEACH Project: Bettering the Evaluation And Care of Health
National, 1998 - Ongoing

The Blue Mountains Eye Study (BMES)
Blue Mountains, NSW, 1992 - Ongoing

The Busselton Health Study
Busselton, WA, 1966 - Ongoing

The Dubbo Study
Dubbo, NSW, 1988 - Ongoing

The Mater-University of Queensland Study of Pregnancy (MUSP)
Brisbane, 1981-2004

The Tasmanian Longitudinal Health Study (TAHS)
National, 1968 - Ongoing

Wittenoom cohort studies
Wittenoom, WA, 1974 - Ongoing

Women's Health Australia (WHA)
National, 1995 - Ongoing

If you are involved in an Australian health longitudinal study which does not appear here, please let us know by emailing phcris@flinders.edu.au and we will add it to this list.

CONDUCTING LONGITUDINAL RESEARCH

Using the Australian Longitudinal Study on Womens Health as a case study, this issue of the International Journal of Multiple Research Approaches is designed as a practical guide to the development and management of longitudinal studies with various articles on topics such as cohort management, data management and dissemination of longitudinal data.

Loxton D, Byles J, Dobson A, Brown W (Eds). (2007). Conducting Longitudinal Research: Practical lessons from the Australian Longitudinal Study on Women's Health, International Journal of Multiple Research Approaches 1(2).

The majority of longitudinal research tends to use predominantly quantitative research methods. This interesting report discusses qualitative longitudinal approaches:

Molloy D, Woodfield K, Bacon J. (2002). Longitudinal qualitative research approaches in evaluation studies, Working Paper Number 7, Department for Work and Pensions, London.

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