Statistical tests for independent groups: time to event data

Researchers assessed the effectiveness of low dose, high frequency ultrasound when combined with standard care in healing venous leg ulcers that had previously been hard to heal. A multicentre randomised controlled trial with a study period of 12 months was performed. Ultrasonography was given for 12 weeks, after which participants returned to standard care alone. Control treatment was standard care alone.[1]

Trial participants were recruited if they had at least one venous leg ulcer of more than six months’ duration or greater than 5 cm² in area and an ankle brachial pressure index >0.8. In total, 168 people were randomised to ultrasound and standard care and 169 to standard care alone. The primary outcome was time from randomisation until healing of the largest eligible leg ulcer, referred to as the reference ulcer. The researchers reported that no significant difference existed between treatment groups in the time until healing of the reference leg ulcer (P=0.61).

Which one of the following …