biostudies-literatureSwets MCMedical Research CouncilNational Institute for Health Research (NIHR)Wellcome Trust7374https://www.ebi.ac.uk/biostudies/studies/S-EPMC10651917biostudies-literatureUnknown14(1)Choosing optimal outcome measures maximizes statistical power, accelerates discovery and improves reliability in early-phase trials. We devised and evaluated a modification to a pragmatic measure of oxygenation function, the [Formula: see text] ratio. Because of the ceiling effect in oxyhaemoglobin saturation, [Formula: see text] ratio ceases to reflect pulmonary oxygenation function at high [Formula: see text] values. We found that the correlation of [Formula: see text] with the reference standard ([Formula: see text]/[Formula: see text] ratio) improves substantially when excluding [Formula: see text] and refer to this measure as [Formula: see text]. Using observational data from 39,765 hospitalised COVID-19 patients, we demonstrate that [Formula: see text] is predictive of mortality, andNature communicationsEvaluation of pragmatic oxygenation measurement as a proxy for Covid-19 severity.PMC10651917NIHR201395NIHR302829215091/Z/18/ZMC_PC_19025DRF-2018-11-ST2-004223164/Z/21/ZMC_PC_20004HDRUK2021.0125216606/Z/19/ZCO-CIN-01Gupta RBaillie JKSwets MCNguyen-Van-Tam JSSemple MGDocherty AMillar JEOpenshaw PSpata EBretherick ADHorby PWLone NKerr SGroeneveld GHDunning JHarrison EHarrison DRowan KMcCurrach FBrown ABStaplin NISARIC4C InvestigatorsYoung NScott-Brown JfalseEvaluation of pragmatic oxygenation measurement as a proxy for Covid-19 severity.Choosing optimal outcome measures maximizes statistical power, accelerates discovery and improves reliability in early-phase trials. We devised and evaluated a modification to a pragmatic measure of oxygenation function, the [Formula: see text] ratio. Because of the ceiling effect in oxyhaemoglobin saturation, [Formula: see text] ratio ceases to reflect pulmonary oxygenation function at high [Formula: see text] values. We found that the correlation of [Formula: see text] with the reference standard ([Formula: see text]/[Formula: see text] ratio) improves substantially when excluding [Formula: see text] and refer to this measure as [Formula: see text]. Using observational data from 39,765 hospitalised COVID-19 patients, we demonstrate that [Formula: see text] is predictive of mortality, and2023-01-01T00:00:00Z2023 Nov2026-06-01T08:13:59.858Z2024-11-14T13:11:18.047ZS-EPMC106519173796826910.1038/s41467-023-42205-6