Table 3.
Fitted mean of sample size and 95% confidence interval (CI) back transformed from logarithmic values, type III F statistic and the corresponding p value of the effect of the covariate on sample size adjusted by class of prevalence, phase of trial and interaction between prevalence and phase
| Characteristics | No. of trials, m | Fitted mean | 95% CI | F test | p value |
|---|---|---|---|---|---|
| Inclusion criteria | |||||
| Gender | 1148 | 10.61 | <.0001 | ||
| Both | 49.30 | (41.85–58.08) | |||
| Female | 58.12 | (44.23–76.38) | |||
| Male | 21.09 | (14.04–31.69) | |||
| Age categories a | 1148 | 4.52 | 0.0004 | ||
| Children only | 36.29 | (28.03–46.99) | |||
| Adults only | 58.49 | (45.34–75.45) | |||
| Elderly only | 89.17 | (58.86–135.08) | |||
| Children and adults | 51.94 | (39.74–67.87) | |||
| Children to elderly | 44.98 | (36.88–54.85) | |||
| Adults to elderly | 50.93 | (42.66–60.80) | |||
| Study designs | |||||
| Has DMC? b | 963 | 9.94 | 0.0017 | ||
| No | 42.95 | (35.92–51.36) | |||
| Yes | 52.43 | (44.06–62.38) | |||
| FDA regulated intervention? c | 1076 | 4.09 | 0.0433 | ||
| No | 52.30 | (43.72–62.56) | |||
| Yes | 46.20 | (38.77–55.06) | |||
| Intervention model | 1114 | 56.55 | <.0001 | ||
| Crossover assignment | 28.63 | (21.84–37.53) | |||
| Factorial assignment | 139.83 | (56.36–346.91) | |||
| Parallel assignment | 71.38 | (60.45–84.28) | |||
| Single group assignment | 34.28 | (29.05–40.46) | |||
| Interventions, facilities and authorities | |||||
| Lead sponsor | 1148 | 1.53 | 0.2041 | ||
| US Federal | 68.43 | (30.81–151.99) | |||
| Industry | 46.20 | (38.50–55.43) | |||
| NIH | 65.80 | (44.80–96.65) | |||
| Other | 49.20 | (41.46–58.38) | |||
| Trial location | 1148 | 7.68 | <.0001 | ||
| US only | 42.50 | (35.57–50.79) | |||
| EU only | 71.63 | (55.99–91.64) | |||
| US and EU | 46.29 | (35.40–60.53) | |||
| Single European country | 49.77 | (41.55–59.62) | |||
| No. of countries involved in the trial | 1148 | 1.07 d | (1.04–1.11) | 16.07 | <.0001 |
| Year that enrolment to the protocol begins | 1141 | 3.14 | 0.0081 | ||
| <1990 | 131.48 | (34.06–507.57) | |||
| 1990–1999 | 57.83 | (41.44–80.69) | |||
| 2000–2004 | 63.10 | (50.12–79.44) | |||
| 2005–2009 | 44.61 | (37.31–53.34) | |||
| 2010–2014 | 48.72 | (40.92–58.01) | |||
| 2015 and after | 49.89 | (35.70–69.71) | |||
| No. of arms | 1085 | 1.39 d | (1.30–1.49) | 83.75 | <.0001 |
a Minimum and maximum age groups are mutually exclusive. Children, term new born infants to adolescents up to 18 years; adults, 18–64 years old; and elderly, 65 years or older
b Indicate whether or not a data monitoring committee (DMC) has been appointed for this study
c Indicate whether or not the trial includes an intervention subject to US Food and Drug Administration regulation under section 351 of the Public Health Service Act or any of the following sections of the Federal Food, Drug and Cosmetic Act: 505, 510(k), 515, 520(m), and 522
d Estimated coefficient, the estimated increase of sample size for every unit increase of the covariate