A blood lead level of 70 mg /ml has been commonly accepted as safe. However, researchers...

A blood lead level of 70 mg /ml has been commonly accepted as safe. However, researchers have noted that some neurophysiological symptoms of lead poisoning appear in people whose blood lead levels are below 70 mg/ml. The article “Subclinical Neuropathy at Safe Levels of Lead Exposure” (Archives of Environmental Health [1975]: 180–183) gave the following nerveconduction velocities for a group of workers who were exposed to lead in the workplace but whose blood lead levels were below 70 mg/ml and for a group of controls who had no exposure to lead:

Use a level .05 rank-sum test to determine whether there is a significant difference in mean conduction velocity between workers exposed to lead and those not exposed to lead.