Editing Longitudinal study (section)

{{short description|Study with repeated observations over time}}
A '''longitudinal study''' (or '''longitudinal survey''', or '''panel study''') is a [[research design]] that involves repeated observations of the same variables (e.g., people) over long periods of time (i.e., uses [[longitudinal data]]). It is often a type of [[observational study]], although it can also be structured as longitudinal [[randomized experiment]].<ref>{{cite book|last1=Shadish|first1=William R.|last2=Cook|first2=Thomas D.|last3=Campbell|first3=Donald T. |title=Experimental and Quasi-Experimental Designs for Generalized Causal Inference|url=https://archive.org/details/experimentalquas00shad|url-access=limited|date=2002|publisher=[[Houghton Mifflin]]|location=Boston, Massachusetts|isbn=0-395-61556-9|page=[https://archive.org/details/experimentalquas00shad/page/n286 267]|edition=2nd}}</ref>

Longitudinal studies are often used in social-personality and [[clinical psychology]], to study rapid fluctuations in behaviors, thoughts, and emotions from moment to moment or day to day; in [[developmental psychology]], to study developmental trends across the life span; and in [[sociology]], to study life events throughout lifetimes or generations; and in [[consumer research]] and [[political polling]] to study consumer trends. The reason for this is that, unlike [[cross-sectional study|cross-sectional studies]], in which different individuals with the same characteristics are compared,<ref>{{cite book |first1=Neil R.|last1=Carlson| first2=Harold L. Jr. |last2=Miller|first3=Donald S.|last3=Heth|first4=John W.|last4=Donahoe|first5=G. Neil|last5=Martin |title=Psychology: the Science of Behavior |publisher=[[Allyn & Bacon]] |location=Boston, Massachusetts|isbn=978-0-205-54786-9 |date=2009|edition=7th | pages = 361 }}</ref> longitudinal studies track the same people, and so the differences observed in those people are less likely to be the result of cultural differences across generations, that is, the [[cohort effect]]. Longitudinal studies thus make observing changes more accurate and 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. 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.

Longitudinal studies can be [[Retrospective study|retrospective]] (looking back in time, thus using existing data such as medical records or claims database) or [[Prospective study|prospective]] (requiring the collection of new data).{{citation needed|date=May 2017}}

[[cohort study|Cohort studies]] are one type of longitudinal study which sample a [[cohort (statistics)|cohort]] (a group of people who share a defining characteristic, typically who experienced a common event in a selected period, such as birth or graduation) and perform [[Cross-sectional data|cross-section]] observations at intervals through time. Not all longitudinal studies are cohort studies; some instead include a group of people who do not share a common event.<ref>{{cite web|url=http://academia.stackexchange.com/questions/54017/what-is-the-difference-between-a-panel-study-and-a-cohort-study|title=What is the difference between a Panel Study and a Cohort Study?|website=Academia Stack Exchange|access-date=3 February 2016}}</ref>

As opposed to observing an entire population, a panel study follows a smaller, selected group - called a 'panel'.<ref>[https://www.studysmarter.co.uk/explanations/social-studies/research-methods-in-sociology/longitudinal-study-sociology/ Longitudinal Study in Sociology.]</ref>