Table 2.
Design characteristics (rationale for ITS, data handling and model structure) of included studies
| Characteristics | n or median | % or IQR |
|---|---|---|
| Rationale for ITS | ||
| Did the author give the reason/rationale for using ITS study design? (N = 153) | ||
| Yes | 43 | 28.1 |
| Clearly segment time? (N = 153) | ||
| Yes | 153 | 100.0 |
| Use of control group (N = 153) | ||
| Yes | 19 | 12.4 |
| Type of control (N = 19)a | ||
| Characteristic | 11 | 57.9 |
| Location | 6 | 31.6 |
| Historical | 1 | 5.3 |
| Outcome | 1 | 5.3 |
| Data collection and aggregation | ||
| Data collection (N = 153) | ||
| Retrospective | 141 | 92.2 |
| Prospective | 12 | 7.8 |
| For studies used prospective data, if they have pre-specified protocol? (N = 12) | ||
| Yes | 2 | 16.7 |
| Raw data (N = 153) | ||
| Contained individual-level data | 127 | 83.0 |
| Only contained aggregated-level data | 26 | 17.0 |
| Analysis unit b (N = 153) | ||
| Aggregated unit | 149 | 97.4 |
| Individual unit | 4 | 2.6 |
| Time intervals used for ITS with aggregated unit (N = 149) | ||
| Month | 110 | 73.8 |
| Quarter | 17 | 11.4 |
| Week | 7 | 4.7 |
| Year | 6 | 4.0 |
| Day | 4 | 2.7 |
| Six-month | 2 | 1.3 |
| Two-week | 2 | 1.3 |
| Two-month | 1 | 0.7 |
| Number of time points (N = 149)c | 48 | 30, 72 |
| Did the author give the rationale for the number of time points? (N = 149) | ||
| Yes | 31 | 20.8 |
| The ITS model structure | ||
| Type of ITS impact model (N = 153) | ||
| Level and slope change | 139 | 90.8 |
| Level change only | 6 | 3.9 |
| Slope change only | 6 | 3.9 |
| Unclear | 2 | 1.3 |
| Did the author give the rationale for using this model? (N = 153) | ||
| Yes | 21 | 13.7 |
| Did the author allow for a delay impact? (N = 153) | ||
| Yes | 42 | 27.5 |
| Methods of dealing with delay (N = 42)d, e | ||
| Sensitivity | 19 | 45.2 |
| Segment | 11 | 26.2 |
| Excluded | 10 | 23.8 |
| Delay | 6 | 14.3 |
| Did the author give the rationale for setting the transition period? (N = 42) | ||
| Yes | 23 | 54.8 |
aLocation: use a different area as control; Outcome: use an outcome not affected by the intervention as control; Characteristic: use a group not targeted by an intervention as control; Historical: compare a previous group to a current group
bAggregated data refer to summary statistics (e.g., mean, percentage, median) calculated across individual data
cWe reported the median and interquartile range (25% and 75%)
dDelay: where the delay was acknowledged and included in pre- or post-interruption segment; Excluded: where a separate segment was used for the delay time period, but this was excluded from the analysis; Segment: where a separate segment was used for the delay time period, and this was included in analysis; Sensitivity: where the delay was modelled as part of a sensitivity analysis, but ignored in main analysis)
eSome studies used more than one method to deal with delay