Interrupted time series

{{short description|Method of analysis involving tracking a long-term period around an intervention}}

Interrupted time series analysis (ITS), sometimes known as quasi-experimental time series analysis, is a method of statistical analysis involving tracking a long-term period before and after a point of intervention to assess the intervention's effects. The time series refers to the data over the period, while the interruption is the intervention, which is a controlled external influence or set of influences.{{Citation|last1=Ferron|first1=John|title=Interrupted Time Series Design|date=2005|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/0470013192.bsa312|encyclopedia=Encyclopedia of Statistics in Behavioral Science|publisher=American Cancer Society|language=en|doi=10.1002/0470013192.bsa312|isbn=978-0-470-01319-9|access-date=2020-03-09|last2=Rendina‐Gobioff|first2=Gianna}}{{Cite book|last1=McDowall|first1=David|url=https://books.google.com/books?id=oAIuJ2JQIngC&pg=PA11|title=Interrupted Time Series Analysis|last2=McCleary|first2=Richard|last3=Meidinger|first3=Errol|last4=Hay|first4=Richard A. Jr.|date=August 1980|publisher=SAGE|isbn=978-0-8039-1493-3|pages=5–6|language=en}} Effects of the intervention are evaluated by changes in the level and slope of the time series and statistical significance of the intervention parameters.Handbook of Psychology, Research Methods in Psychology, [https://books.google.com/books?id=MnOyiy5dtSsC&pg=PA582 p. 582] Interrupted time series design is the design of experiments based on the interrupted time series approach.

The method is used in various areas of research, such as:

• political science: impact of changes in laws on the behavior of people; (e.g., Effectiveness of sex offender registration policies in the United States)
• economics: impact of changes in credit controls on borrowing behavior;
• sociology: impact of experiments in income maintenance on the behavior of participants in welfare programs;
• history: impact of major historical events on the behavior of those affected by the events;
• psychology: impact of expressing emotional experiences on online content;{{cite journal|last1=Bollen|display-authors=et al|title=The minute-scale dynamics of online emotions reveal the effects of affect labeling|journal=Nature Human Behaviour|date=2019|volume=3|issue=1 |pages=92–100|url=https://www.nature.com/articles/s41562-018-0490-5|doi=10.1038/s41562-018-0490-5|pmid=30932057 |s2cid=56399577 }}
• medicine: in medical research, medical treatment is an intervention whose effect are to be studied;
• marketing research: to analyze the effect of "designed market interventions" (e.g., advertising) on sales.{{cite journal |last1=Brodersen |display-authors=et al |title=Inferring causal impact using Bayesian structural time-series models |journal=Annals of Applied Statistics |date=2015 |volume=9 |pages=247–274 |doi=10.1214/14-AOAS788 |arxiv=1506.00356 |s2cid=2879370 |url=https://ai.google/research/pubs/pub41854 |access-date=21 March 2019}}
• environmental sciences: impacts of human activities on environmental quality and ecosystem dynamics (e.g., forest logging on local climate).{{cite journal |last1=Li |first1=Yang |last2=Liu |first2=Yanlan |last3=Bohrer |first3=Gil |last4=Cai |first4=Yongyang |last5=Wilson |first5=Aaron |last6=Hu |first6=Tongxi |last7=Wang |first7=Zhihao |last8=Zhao |first8=Kaiguang |title=Impacts of forest loss on local climate across the conterminous United States: Evidence from satellite time-series observation |journal=Science of the Total Environment |date=2022 |volume=802 |page=149651 |doi=10.1016/j.scitotenv.2021.149651 |pmid=34525747 |bibcode=2022ScTEn.802n9651L |url=https://u.osu.edu/agroecosystemresilience/files/2021/09/Li_etal.pdf}}{{cite web |last1=Li |first1=Yang |last2=Zhao |first2=Kaiguang |last3=Hu |first3=Tongxi |last4=Zhang |first4=Xuesong |title=BEAST: A Bayesian Ensemble Algorithm for Change-Point Detection and Time Series Decomposition |website=GitHub |url=https://github.com/zhaokg/Rbeast}}