Longitudinal study
Encyclopedia
A longitudinal study is a correlation
al 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
, 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 experiment
s. 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.
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 not possible 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.
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
al 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
Observational study
In epidemiology and statistics, an observational study draws inferences about the possible effect of a treatment on subjects, where the assignment of subjects into a treated group versus a control group is outside the control of the investigator...
. Longitudinal studies are often used in psychology to study developmental trends across the life span, and in sociology
Sociology
Sociology is the study of society. It is a social science—a term with which it is sometimes synonymous—which uses various methods of empirical investigation and critical analysis to develop a body of knowledge about human social activity...
to study life events throughout lifetimes or generations. The reason for this is that unlike cross-sectional studies
Cross-sectional study
Cross-sectional studies form a class of research methods that involve observation of all of a population, or a representative subset, at one specific point in time...
, 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
Observational science
An observational science is a science where it is not possible to construct controlled experiments in the area under study. For example, in astronomy, it is not possible to create or manipulate stars or galaxies in order to observe what happens...
, 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
Causality
Causality is the relationship between an event and a second event , where the second event is understood as a consequence of the first....
than do experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
s. 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.
Longitudinal studies allow social scientists to distinguish short from long-term phenomena, such as poverty
Poverty
Poverty is the lack of a certain amount of material possessions or money. Absolute poverty or destitution is inability to afford basic human needs, which commonly includes clean and fresh water, nutrition, health care, education, clothing and shelter. About 1.7 billion people are estimated to live...
. 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 not possible to conclude which of these possibilities is the case using one-off cross-sectional studies.
Types of longitudinal studies include cohort studies
Cohort study
A cohort study or panel study is a form of longitudinal study used in medicine, social science, actuarial science, and ecology. It is an analysis of risk factors and follows a group of people who do not have the disease, and uses correlations to determine the absolute risk of subject contraction...
and panel studies. Cohort studies
Cohort study
A cohort study or panel study is a form of longitudinal study used in medicine, social science, actuarial science, and ecology. It is an analysis of risk factors and follows a group of people who do not have the disease, and uses correlations to determine the absolute risk of subject contraction...
sample a cohort
Cohort (statistics)
In statistics and demography, a cohort is a group of subjects who have shared a particular time together during a particular time span . Cohorts may be tracked over extended periods in a cohort study. The cohort can be modified by censoring, i.e...
, 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.
Examples
- Avon Longitudinal Study of Parents and ChildrenAvon Longitudinal Study of Parents and ChildrenThe Avon Longitudinal Study of Parents and Children, also known as Children of the 90s and formerly the Avon Longitudinal Study of Pregnancy and Childhood, is a cohort study of children born in the former county of Avon, England during 1991 and 1992...
(ALSPAC) - Born in BradfordBorn in BradfordBorn in Bradford is a large birth cohort study based at Bradford Royal Infirmary, a hospital in the city of Bradford, West Yorkshire in the United Kingdom...
- 1970 British Cohort Study1970 British Cohort StudyThe 1970 British Cohort Study is a continuing, multi-disciplinary longitudinal survey monitoring the development of babies born in the UK in one particular week in April 1970.-History:...
(BCS70) - British Household Panel SurveyBritish Household Panel SurveyThe British Household Panel Survey , carried out at the Institute for Social and Economic Research of the University of Essex, is an instrument for social and economic research. A sample of British households was drawn and first interviewed in 1991. The members of these original households have...
- Busselton Health Study
- Canadian Longitudinal Study
- Child Development Project
- Children of Immigrants Longitudinal Study (CILS)
- Dunedin Multidisciplinary Health and Development StudyDunedin Multidisciplinary Health and Development StudyThe Dunedin Multidisciplinary Health and Development Study is a long-running cohort study of 1037 people born over the course of a year in Dunedin, New Zealand....
- Fragile Families and Child Wellbeing StudyFragile Families and Child Wellbeing StudyThe Fragile Families and Child Wellbeing Study is a longitudinal birth cohort study of American children in urban areas, run by Princeton University and Columbia University. It uses a stratified random sample technique and an oversample of non-marital births. Baseline data collection ran from...
- Framingham Heart StudyFramingham Heart StudyThe Framingham Heart Study is a long-term, ongoing cardiovascular study on residents of the town of Framingham, Massachusetts. The study began in 1948 with 5,209 adult subjects from Framingham, and is now on its third generation of participants...
- Genetic Studies of GeniusGenetic Studies of GeniusThe Genetic Studies of Genius, today known as the Terman Study of the Gifted, is a still-running longitudinal study begun in 1921 to examine the development and characteristics of gifted children into adulthood...
(the world's oldest and longest-running longitudinal study) - German Socio-Economic Panel (SOEP)
- Health and Retirement StudyHealth and Retirement StudyThe Health and Retirement Study is conducted by the at the University of Michigan in Ann Arbor and supported by the National Institute on Aging . The study interviews 22,000 Americans 50 and over every two years on subjects like health care, housing, assets, pensions , employment and...
- Household, Income and Labour Dynamics in Australia SurveyHousehold, Income and Labour Dynamics in Australia SurveyThe Household, Income and Labour Dynamics in Australia survey is an Australian household-based panel study which began in 2001. It has been used for examining issues such as the incidence of persistent poverty; assets and income in the transition to retirement; the correlates and impact of...
- Human speechome projectHuman speechome projectThe Human Speechome Project, , is an effort to closely observe and model the language acquisition of a child over the first three years of life....
- Luxembourg Income Study (LIS)
- Millennium Cohort StudyMillennium Cohort StudyThe Millennium Cohort Study is a longitudinal survey conducted by the Centre for Longitudinal Studies at the University of London, following the lives of a sample of about 19,000 babies born in the UK in the year 2000–2001.-History:...
(MCS) - Millennium Cohort Study (United States)
- Minnesota Twin Family StudyMinnesota Twin Family StudyThe Minnesota Twin Family Study is a longitudinal study of twins conducted by researchers at the University of Minnesota - Twin Cities. It seeks to identify the genetic and environmental influences on the development of psychological traits....
- National Child Development StudyNational Child Development StudyThe National Child Development Study is a continuing, multi-disciplinary longitudinal study which follows the lives of about 17,000 people born in Great Britain in a certain week in 1958.-History:...
(NCDS) - National Longitudinal Study of Children and Youth (NLSCY)
- Pacific Islands Families StudyPacific Islands Families StudyThe Pacific Islands Families Study is a long-running, cohort study of 1398 children of Pacific Islands origin born in Auckland, New Zealand during the year 2000....
- Panel Study of Belgian Households
- Rotterdam StudyRotterdam StudyThe Rotterdam Study is a prospective, population-based cohort study. The aim of the Rotterdam Study is to investigate factors that determine the occurrence of cardiovascular, neurological, ophthalmological, endocrinological, and psychiatric diseases in elderly people.The study was established in...
- Seattle Longitudinal StudyK. Warner SchaieK. Warner Schaie, Ph.D. is an American social gerontologist and psychologist best known for co-founding the Seattle Longitudinal Study in 1956....
- Up Series
- WHO's Study on global AGEing and adult health (SAGE)
- Wisconsin Longitudinal Study