Simple scientific questions require simple scientific answers; doctors want unequivocal guidance to their practice so that they do not fumble in the dark. But it is easier to ask questions than to answer them, as two papers published in the same week in the New England Journal of Medicine and the Journal of the American Medical Association attest.

The question asked by the two papers was the optimum level of oxygenation in the blood of pre-term infants. In the past it was rather naively supposed that if oxygen were necessary, then more of it must be better; but premature infants who were exposed to high levels of oxygen developed a condition known as retinopathy of prematurity, often leaving them blind or severely impaired visually.

The two trials, one from Britain, Australia and New Zealand, and the other from the United States, Canada, Argentina, Finland, Germany and Israel, sought to establish whether a higher or lower level of oxygen saturation of the blood was better for infants born very prematurely. The results were different, if not quite diametrically opposed.

The first trial found that babies treated so that their blood oxygen saturation was higher had a lower death rate at 36 weeks than those treated so that their levels were lower. 15.9 percent in the high-saturation group died compared with 23.1 per cent in the lower. You would have to treat 14 babies with the high oxygen saturation to save life more than treating them at the lower level.