Table 2 Statistical design features of 52 clinical trials that stopped for futility

Type of primary outcome

Binary/ Continuous/ time-to-event/ Trinomial

33/ 10/ 8/ 1

Planned sample size

Median (IQR)

209 (133–586)

Study power %

70–79 / 80–89 / 90 + / Unclear

1 / 32 / 15 / 4

Interim analyses planned?

Yes / No / Not stated

38 / 6 / 8

Number of interim analyses for futility planned

1 / 2 / 3 / Other ^a / Not stated

19 / 5 / 2 / 3 / 9

Basis for stopping rule

Not defined / Threshold / p-value / CP-related / Other

30 / 9 / 4 / 5 / 4

Information % at planned IA^b

<  40 / 40–59 / 60–79 / Not stated or unclear / Other

7 / 17 / 9 / 19 / 4

Number of actual interim analyses

0 / 1 / 2 / Other^c

2 / 41 / 7 / 2

Type of significance testing

One-sided / Two-sided / Unclear

14 / 33 / 5