The nonlinear coupling coefficient and the energy transfer associated with three‐wave interactions are computed from measured data of the turbulent edge plasma of the Texas Experimental Tokamak(TEXT) [Nucl. Technol. Fusion1, 479 (1981)]. The results show the presence of three‐wave interactions. The interactions cause energy to cascade away from the dominant waves of the spectrum primarily toward lower, but also toward higher frequencies. The results are obtained with a new digital spectral analysis technique based on the estimation of higher‐order cumulants. The method is discussed and tested on a simulation experiment. The same technique is useful for neutral fluids as well.