Observations of the electron density n_e based on measurement of the upper hybrid resonance frequency by the Polar spacecraft Plasma Wave Instrument (PWI) are available for March, 1996 to September, 1997, during which time the Polar orbit sampled all MLT values three times. Using this data set, we assume a power law form for the electron density dependence along field lines n_e = n_e0 (R_max/R)^α, where n_e0 is the equatorial electron density and R_max ≈ LR_E is the maximum geocentric radius R to any point on the field line, and model the statistical average of α as α_model = 8.0 − 3.0 log₁₀n_e0 + 0.28 (log₁₀n_e0)² − 0.43(R_max/R_E) for all categories of plasma (plasmasphere and plasmatrough), with an average error of 0.65. The data set on which this result is based is limited to 2.5R_E ≤ R_max ≤ 8.5R_E, 2R_E ≤ R ≤ R_max, and 2 ≤ n_e0 ≤ 1500 cm⁻³. There is no remaining dependence of the average α – α_model on MLT or Kp.