Figure 1. Predicted probability of apnea in recovery room and postrecovery room by weeks postconceptual age for all patients for each investigator. Bottom marks indicate the number of data points versus postconceptual age. The curves for the Kurth et al. and Welborn et al. studies are nearly identical in the upper range, and for the Malviya et al. and Warner et al. studies, in the lower range. There was significant institution-to-institution variability. The reasons for this are unclear but may represent differences in monitoring technology as well as patient populations, because the studies with the highest rate of apnea were also those that used continuous recording devices. See text for further discussion.