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Table 2 Characteristics of interrupted time series studies and series

From: Comparison of six statistical methods for interrupted time series studies: empirical evaluation of 190 published series

Study level characteristics All ITS studies
(n = 200)
ITS studies with available
data (n = 166)
n % n %
Type of interruption
Exposurea 12 6 10 6
Intervention 188 94 156 94
Intervention type
Policy change 104 52 82 49
Practice change 40 20 36 22
Communication 29 15 24 14
Organisation of care 13 7 12 7
Clinical intervention 2 1 2 1
Time interval type
Daily 3 2 2 1
Weekly 9 5 6 4
Two weekly 1 1 1 1
Monthly 120 60 96 58
Quarterly 31 16 28 17
Six monthly 3 2 3 2
Annually 20 10 17 10
Other 12 6 12 7
Can't determine 1 1 1 1
Series level characteristics ITS
(n = 230)
ITS with available data
(n = 190)
median IQR median IQR
Number of time points per series 48 (30, 100) 41 (25, 71)
Number of time points in the segments used to calculate estimates for the first interruption 18 (10, 34) 16 (10, 28)
  1. Abbreviations: ITS Interrupted time series, IQR Inter-quartile range
  2. aOur definition of an exposure is limited to exposures or events that are not under investigator control (e.g. earthquakes, financial crises, tsunamis, environmental chemicals). We use the term ‘investigator’ loosely to include researchers, clinicians and policy makers