Breast Cancer and Magnetic Fields Data Description
The data set consists of 813 cases of breast cancer and 793 controls from November 1992 and March 1995 in the Seattle area. The data was obtained from the Cancer Surveillance System of the Fred Hutchison Cancer Research Center. The patient age, ranging from 20 to 74 and divided into six age-groups, and mean of 48-hour continuous measurements of magnetic field levels in each patient's bedroom. 

Variables included in the Dataset: 
Y: Indicator of breast cancer 
agegrp: Patient age group 
L: ??? 
mnmag: Mean of 48-hour continuous measurements of magnetic field levels in each patient's bedroom