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The applicability of several frequency scaling methods of rain attenuation is discussed based upon the cumulative distributions of rain attenuations at 81.8, 34.5, and 11.5 GHz measured in the same horizontal propagation path of 1.3 km for 1 year. A frequency scaling method (MISD) based upon the concept of a path-averaged raindrop size distribution N(D) is newly applied to statistical prediction of the attenuation and is shown to be effective at millimeter wave bands where attenuation changes remarkably depending upon the raindrop size distribution, although the usefulness of MISD has been verified for time-sequential data. The size distribution determined from the statistical data at the three frequencies is given by N(D) = 26,000 R(−0.294)exp [−(5.6 R−0.283D)], 10 ≤ R ≤ 70 mm/h, where R is the path-averaged rainfall rate in millimeters per hour and D is the diameter of a raindrop in millimeters. Frequency dependence of attenuation calculated by using this size distribution shows that the prediction of rain attenuation based upon the Laws and Parsons size distribution results in an underestimation at frequencies above 80 GHz.