We have studied, using linear cross correlation and multilinear regression analyses, statistical relations between the magnetospheric auroral electrojet intensity index AE and various parameters characterizing the interplanetary plasma and magnetic field. We also consider the recently proposed &egr; parameter as an independent variable. The analyses were carried out separately for twenty-eight days in mid 1975 and for each of five individual magnetic storm intervals that have been previously discussed extensively in the literature. We find that when the interplanetary data set is not distinguished as to the direction of the north-south component Bz, the interplanetary electric field -VBz carried to the front of the magnetosphere correlates with AE substantially better than does &egr;. Considering only data during which Bz is negative gives a slightly better correlation of &egr; with AE than of the electric field with AE. The correlations are valid for the specific storm periods as well as for the unrestricted twenty-eight days of data. Our results suggest that the physical processes involved in energy transfer to the nightside magnetosphere depend upon the direction of the north-south component of the interplanetary magnetic field: the interplanetary electric field plays an important role during northward Bz and the &egr; parameter and the electric field both provide an indication of energy transfer and substorm activity during southward Bz.