Treatment allocation by minimisation

Researchers assessed the effectiveness of adenoidectomy in children with recurrent upper respiratory tract infections. An open randomised controlled trial study design was used. The intervention was immediate adenoidectomy, with or without myringotomy. Control treatment was a strategy of initial watchful waiting.1

The trial participants were 111 children aged 1-6 years with recurrent upper respiratory tract infections who had been selected for adenoidectomy. Participants were recruited from 13 sites, including 11 general hospitals and two academic centres. Children were allocated to treatment using minimisation to control for age (<2 and ≥2 years) and site of recruitment. Length of follow-up was a maximum of 24 months.

The primary outcome measure was the number of upper respiratory tract infections per person year during follow-up. No significant difference was seen between treatment groups, with 7.91 episodes of upper respiratory tract infections per person year in the adenoidectomy group and 7.84 in the control group (difference in incidence rate 0.07, 95% confidence interval −0.70 to 0.85). It was concluded that in children selected for adenoidectomy with recurrent upper respiratory tract infections, immediate surgery confers no clinical benefits over a strategy of initial watchful waiting.

Which of the following statements, if any, are true?

• a) Minimisation was used to achieve a balance in the numbers of participants and baseline characteristics between treatment groups

• b) Each participant had an equal probability of being allocated to the intervention or control group.

• c) For each participant recruited to the trial, treatment allocation depended on his or her individual characteristics