6.13 Blood-chilling and strokes. A Science News article reported a study of the effect of cooling the blood of stroke patients on the extent of recovery 90 days after the stroke. Researchers randomly assigned 58 severe-stroke patients to receive either tPA (the standard treatment for stroke) or tPA plus blood-chilling. Regulators overseeing the study required a one-hour delay from the point at which tPA was given before cooling could be started. The researchers found no significant difference in the effects of the two treatments on recovery. Researchers also noted that the recovery rate for both groups was worse than the average seen in stroke patients nationwide but were not concerned. Why were they unconcerned?