Table 2. Description of the covariates included in the meta-regression analyses (n = 32 studies with 44 coefficients).
| Variable (metric) | Range | Mean | Standard Deviation |
| Number of manuscripts | 15→1983 | 321.98 | 398.13 |
| Variable (categorical) | Range | Frequency | Percent |
| Method: | |||
| ICC | 0–1 | 35 | 80 |
| r (RC) | 0–1 | 9 | 20 |
| Discipline: | |||
| Economics/Law | 0–1 | 3 | 7 |
| Natural Sciences | 0–1 | 7 | 16 |
| Medical Sciences | 0–1 | 11 | 25 |
| Social Sciences (RC) | 0–1 | 23 | 52 |
| Object of appraisal: | |||
| Paper | 0–1 | 29 | 66 |
| Abstract (RC) | 0–1 | 15 | 34 |
| Cohort: | |||
| 1950–1979 | 0–1 | 15 | 34 |
| 1980–1989 | 0–1 | 9 | 21 |
| 1990–1999 | 0–1 | 5 | 11 |
| 2000–2008 | 0–1 | 8 | 18 |
| Unknown (RC) | 0–1 | 7 | 16 |
| Blinding: | |||
| Single | 0–1 | 22 | 50 |
| Double | 0–1 | 3 | 7 |
| Unknown (RC) | 0–1 | 19 | 43 |
| Rating System:* | |||
| Categorical | 0–1 | 35 | 80 |
| Metric | 0–1 | 5 | 11 |
| Unknown (RC) | 0–1 | 4 | 9 |
Note: RC = reference category in meta-regression analysis. Unknown = this information is missing in a study.
*Rating systems are classified as categorical, if they have nine or fewer categories; in case of more than nine categories, the classification is made as metric [110].