Table 1.

Description of Studies Included in the Review with Respect to Methods Used in the Analysis of ITS Data

Characteristic	Number of Studies Included in the Review, N, (%) *N= 1389
Methods papers	24 (1.73)
Novel methods	11 (45.8)
Method adaptation and important contribution	7 (29.2)
Method comparison	6 (25.0)
Application papers	1365 (98.27)
Field of Application
Clinical	621 (45.5)
Pharmaceutical	238 (17.4)
Guideline implementation	69 (5.1)
Public health/policy	437 (32.0)
Setting/Design
Single site	353 (25.9)
Multiple baseline/multi-site	392 (28.7)
Controlled ITS	237 (17.4)
National (population study)	383 (28.1)
Statistical Methods Used in Articles
Segmented Regression
Segmented regression using linear models	360 (26.4)
Segmented regression using GLM, GEE or GAM**	261 (19.1)
Segmented regression using ARIMA	268 (19.6)
Non-segmented regression	110 (19.6)
Non-regression methods eg t-test	82 (6.0)
Difference in differences	17 (1.2)
Unspecified	267 (19.6)
Type of Outcome of Interest
Continuous	131 (9.6)
Count	1029 (75.4)
Binary	205 (15.0)
Number of Time Points
Less than 16 (or < 8 per period)	141 (10.3)
At least 16 (or ≥ 8 per period)	634 (46.5)
At least 50	590 (43.2)
Autocorrelation Checked
Yes	812 (59.5)
Other Biases Checked
Yes	607 (44.5)
Specific Biases***
Seasonality	407 (67.1)
Non-stationarity	290 (47.8)
Heteroskedasticity	123 (20.3)
Confounding	203 (33.4)
Clustering	68 (11.2)
Presentation of ITS Results
Figures	414 (30.3)
Tables	105 (7.7)
Both	804 (58.9)
None	42 (3.1)

Notes: *All percentages are out of the total number of corresponding papers. **ITS- interrupted time series; GLM – Generalized Linear Models; GAM – Generalized Additive Models; GEE – Generalized Estimating Equation. ***The frequencies and percentages are out of the total of 607.