Table 4

 Estimated sample sizes for two sided and one sided testing, based on the chronological placebo event rates, calculated for five hypothetical situations: drugs working according to the RRR model (two), the ARR model (two), and a mixed model (one)

RRR constantARR constantMixed model
Placebo event rate(%)RRR = 50%RRR = 75%ARR = 15%ARR = 25%Intervention event rate = 5%
Patient group2 sided1 sided2 sided1 sided2 sided1 sided2 sided1 sided2 sided1 sided
Early RA, disease duration <2 years; late RA: disease duration ⩾2 years; RRR, relative risk reduction = (1−(negative event rate intervention group – negative event rate placebo group)×100); ARR, attributive risk reduction = (negative event rate placebo group – negative event rate intervention group); event rate, percentage of patients with progression of joint damage larger than smallest detectable change (SDC) based on the chronological Sharp/van der Heijde change-score.
*ARR 25% not feasible owing to a placebo event rate <25%, estimated sample size based on the maximal ARR (18%).
Early RA
Regardless of baseline damage182271798466604837*29*9474
Medium + high baseline damage, score ⩾4359776362813510624192520
High baseline damage, score ⩾216434271310168132403275
Late RA
Regardless of baseline damage369273342713810925202318
Medium + high baseline damage, score⩾4427358272115412231241714
High baseline damage, score ⩾2152524119151691333729119