Using intervention time series analyses to assess the effects of imperfectly identifiable natural events: a general method and example.
BACKGROUND
Intervention time series analysis (ITSA) is an important method for analysing the effect of sudden events on time series data. ITSA methods are quasi-experimental in nature and the validity of modelling with these methods depends upon assumptions about the timing of the intervention and the response of the process to it.


METHODS
This paper describes how to apply ITSA to analyse the impact of unplanned events on time series when the timing of the event is not accurately known, and so the problems of ITSA methods are magnified by uncertainty in the point of onset of the unplanned intervention.


RESULTS
The methods are illustrated using the example of the Australian Heroin Shortage of 2001, which provided an opportunity to study the health and social consequences of an abrupt change in heroin availability in an environment of widespread harm reduction measures.


CONCLUSIONS
Application of these methods enables valuable insights about the consequences of unplanned and poorly identified interventions while minimising the risk of spurious results.
Gilmour
Stuart
S
National Drug and Alcohol Research Centre, University of New South Wales, Sydney, NSW 2052, Australia. stuart.gilmour@unsw.edu.au
Degenhardt
Louisa
L
Hall
Wayne
W
Day
Carolyn
C
D001315:Australia; D004335:Drug and Narcotic Control; D003932:Heroin / Q000191:economics / Q000600:supply & distribution; D006801:Humans; D013287:Illicit Drugs / Q000191:economics / Q000600:supply & distribution; D015233:Models, Statistical; D016012:Poisson Distribution; D011159:Population Surveillance / Q000379:methods*; D015985:Precipitating Factors; D011640:Public Policy; D018570:Risk Assessment / Q000379:methods*; D012922:Social Change; D013997:Time Factors; D035501:Uncertainty
D013287:Illicit Drugs; D003932:Heroin