A longitudinal survey is a correlational research study that involves repeated observations of the same variables over long periods of time — often many decades. It is a type of observational study. Longitudinal studies are often used in psychology to study developmental trends across the life span, and in sociology to study life events throughout lifetimes or generations. The reason for this is that, unlike cross-sectional studies, in which different individuals with same characteristics are compared, longitudinal studies track the same people, and therefore the differences observed in those people are less likely to be the result of cultural differences across generations. Because of this benefit, longitudinal studies make observing changes more accurate, and they are applied in various other fields. In medicine, the design is used to uncover predictors of certain diseases. In advertising, the design is used to identify the changes that advertising has produced in the attitudes and behaviors of those within the target audience who have seen the advertising campaign.
Because most longitudinal studies are observational, in the sense that they observe the state of the world without manipulating it, it has been argued that they may have less power to detect causal relationships than do experiments. But because of the repeated observation at the individual level, they have more power than cross-sectional observational studies, by virtue of being able to exclude time-invariant unobserved individual differences, and by virtue of observing the temporal order of events. Some of the disadvantages of longitudinal study include the fact that they take a lot of time and are very expensive. Therefore, they are not very convenient.
Longitudinal studies allow social scientists to distinguish short from long-term phenomena, such as poverty. If the poverty rate is 10% at a point in time, this may mean that 10% of the population are always poor, or that the whole population experiences poverty for 10% of the time. It is impossible to conclude which of these possibilities is the case using one-off cross-sectional studies.
Types of longitudinal studies include cohort studies and panel studies. Cohort studies sample a cohort, defined as a group experiencing some event (typically birth) in a selected time period, and studying them at intervals through time. Panel studies sample a cross-section, and survey it at (usually regular) intervals.
A retrospective study is a longitudinal study that looks back in time. For instance, a researcher may look up the medical records of previous years to look for a trend.
|Study name||Type||Country or Region||Year started||Participants||Remarks|
|Alzheimer's Disease Neuroimaging Initiative||Panel||International||2004||n/a||-|
|Avon Longitudinal Study of Parents and Children (ALSPAC)||Cohort||United Kingdom||1991||14,000||-|
|Born in Bradford||Cohort||United Kingdom||2007||12,500||-|
|1970 British Cohort Study (BCS70)||Cohort||United Kingdom||1970||17,000||Monitors the development of babies born in the UK in one particular week in April 1970|
|British Household Panel Survey||Panel||United Kingdom||1991||n/a||Modeled on the US PFID study|
|Busselton Health Study||Panel||Australia||1966||10,000||-|
|Caerphilly Heart Disease Study||Cohort||United Kingdom||1979||2,512||Male subjects (Wales)|
|Canadian Longitudinal Study on Aging (CLSA-ÉLCV)||Cohort||Canada||2012||50,000||Planned as a 20-year study.|
|Child Development Project||Cohort||United States||1987||585||Follows children recruited the year before they entered kindergarten in three cities: Nashville and Knoxville, TN and Bloomington, Indiana|
|Children of Immigrants Longitudinal Study (CILS)||Cohort||United States||1992||5,262||Florida|
|Congenital Heart Surgeons' Society (CHSS)||Cohort||Canada||-||5,000||Various studies, managed by the Data Center Studies on Congenital Heart Diseases|
|Dunedin Multidisciplinary Health and Development Study||Cohort||New Zealand||1972||1,037||Participants were all born in 1972|
|Study of migrants and squatters in Rio’s Favelas||Cohort||Brazil||1968||n/a||The work of Janice Perlman, reported in her book, Favela (2014)|
|Fragile Families and Child Wellbeing Study||Cohort||United States||1998||n/a||Study being conducted in 20 cities|
|Framingham Heart Study||Cohort||United States||1948||5,209||Massachusetts|
|Genetic Studies of Genius||Cohort||United States||1921||1,528||The world's oldest and longest-running longitudinal study|
|Socio-Economic Panel (SOEP)||Panel||Germany||1984||12,000||-|
|Growing Up in Scotland (GUS)||Cohort||United Kingdom||2003||14,000||Scotland|
|Health and Retirement Study||Cohort||United States||1988||22,000||-|
|Household, Income and Labour Dynamics in Australia Survey||Panel||Australia||2001||25,000||-|
|Human Speechome Project||Cohort||United States||2005||1||Single participant was the son of the researcher, studying language development. Project concluded in 2008.|
|Study of Australian Children||Cohort||Australia||2004||10,000||-|
|Luxembourg Income Study (LIS)||Cohort||International||1983||n/a||30 countries|
|Midlife in the United States||Cohort||United States||1983||6,500||-|
|Millennium Cohort Study (MCS)||Cohort||United Kingdom||2000||19,000||Study of child development, social stratification and family life|
|Millennium Cohort Study||Cohort||United States||2000||200,000||Evaluation of long-term health effects of military service, including deployments|
|Minnesota Twin Family Study||Cohort||United States||1983||17,000 (8,500 twin pairs)||-|
|National Child Development Study (NCDS)||Cohort||United Kingdom||1958||17,000||-|
|National Longitudinal Surveys (NLS)||Cohort||United States||1979||NLSY79-12,686, NLSY97-approx. 9000||Icludes 4 Cohorts: NLSY79 (Born 1957-64), NLSY97 (Born 1980-84), NLSY79 Children and Young Adults, National Longitudinal Surveys of Young Women and Mature Women (NLSW)|
|National Longitudinal Survey of Children and Youth (NLSCY)||Cohort||Canada||1994||35,795||-|
|Pacific Islands Families Study||Cohort||New Zealand||2000||1,398||-|
|Panel Study of Belgian Households||Panel||Belgium||1992||11,000||-|
|Panel Study of Income Dynamics||Panel||United States||1968||70,000||Possibly the oldest household longitudinal surveys in the US|
|Rotterdam Study||Cohort||Netherlands||1990||15,000||Focus is on inhabitants of Ommoord, a suburb of Rotterdam|
|Seattle 500 Study||Cohort||United States||1974||500||Study of the effects of prenatal health habits on human development|
|Study of Health in Pomerania||Cohort||Germany||1997||15,000||Investigates common risk factors, sub-clinical disorders and manifest diseases in a high-risk population|
|Irish Longitudinal Study on Ageing (TILDA)||Cohort||Ireland||2009||8,500||Studies health, social and financial circumstances of older Irish population|
|New Zealand Attitudes and Values Study||-||New Zealand||2009||n/a||-|
|Seattle Longitudinal Study||Cohort||United States||1956||6,000 ||-|
|Understanding Society: The UK Household Longitudinal Study||Panel||United Kingdom||2009||100,000||Incorporates the British Household Panel Survey|
|Up Series||Cohort||United Kingdom||1964||14||Documentary film project by Michael Apted|
|Study on Global Ageing and Adult Health (SAGE)||Cohort||International||2002||65,964||Studies the health and well-being of adult populations and the ageing process in six countries: China, Ghana, India, Mexico, Russian Federation and South Africa|
|Wisconsin Longitudinal Study||Cohort||United States||1957||10,317||Follows graduates from Wisconsin high schools in 1957|
- Carlson, Neil and et al. "Psychology the Science of Behavior", p. 361. Pearson Canada, United States of America
- Cherry, Kendra. "What Is Longitudinal Research?". experiments. About.com guide. Retrieved 22 February 2012.
- Teotonio, Isabel (24 April 2012). "Landmark study on aging to follow 50,000 Canadians over the next two decades". Toronto Life (Toronto Star Newspapers Ltd.). Retrieved 28 July 2014.
- Favela: Longitudinal Multi-Generational Study of migrants and squatters in Rio’s Favelas, 1968-2014
- Growing Up in Scotland, Study dsign
- Panel Study of Belgian Households, Survey summary
- About the Seattle Longitudinal Study