 The study uses a non-inferiority design. Demonstrating superiority of ketamine was not an option based on the number of patients needed to gain sufficient power with such a design. Also, the investigators do not believe that ketamine treatment needs to be more effective, at least not in terms of the primary outcome. ECT is associated with side effects in particular amnesia during the treatment period, but some patients also report persistent memory problems and patients need to be anaesthetised under the supervision of a anaesthesiologist. The treatment is thus fairly demanding and expensive. A significant amount of patients are also unwilling to undergo ECT. Given non- inferiority of ketamine regarding the primary outcome, and given that it is associated with fewer side effects or shorter time to remission and does not involve the need for anaesthesia, in a risk-benefit analysis the scale might be tipped in favour of ketamine, even if it is not superior per se. 