The fluctuations in the cosmic microwave background radiation may contain deviations from gaussian statistics which would be reflected in a nonzero value of three-point correlation function of Δ T. However, any potential observation of the three-point function is limited by cosmic variance, even if a whole-sky map of Δ T is available. Here I derive a general formula for the cosmic variance of the three-point function in terms of integrals over the two-point function. This formula can be applied to any cosmological model and to any experimental measurement strategy. It gives a fundamental lower limit on the magnitude of a measurable three-point correlation function, and hence on the measurable amount of skewness in the distribution of Δ T.
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A 1993 study studied this question.