In reply: Bias risk in systematic reviews

[...]the RoB 2 tool calculates bias in the measurement of the outcome in light of several additional considerations [4]: whether measurement or ascertainment of the outcome differs – or could differ – between intervention groups; who the outcome assessor is, and whether this assessor is blinded to intervention assignment; and whether the assessment of outcome is likely to be influenced by any knowledge of the intervention. Heydari et al stated that patients randomized to receive ketamine were administered a dose of 4mg/kg calculated by their estimated weight at a concentration of 50mg/mL, whereas those randomized to receive haloperidol were administered a fixed dose of 5mg at a concentration of 5mg/mL [5]. Heydari et al provided no information that would have allowed us to evaluate the likelihood of probable knowledge of the intervention impacting assessment of the outcome, so the RoB 2 tool calculated that the measurement of the outcome domain (and therefore the overall study) was at a high risk of bias in accordance with the prespecified algorithm [4].