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Number of different variables reported and their corresponding frequency of occurrence in the 46 publications reviewed.
| Number of variables | Number of occurrences | % of variable occurrences | |
|---|---|---|---|
| Intervals | 100 | 220 | 0.72 |
| Durations | 8 | 61 | 0.20 |
| Partial Durations | 11 | 23 | 0.08 |
| TOTAL | 119 | 304 |
