A theorem first stated by E. C. Fieller in 1940. Suppose that the random variables X and Y have expected values μx and μy , respectively, and a bivariate normal distribution (see multivariate normal distribution). The quantity of interest is γ, the ratio of the two expected values:Let x̄ and y¯ be estimates (see estimator) of μx and μy, respectively, and let the respective estimates of the variances and covariance be denoted by sx2, sy2 and cxy, with ν degrees of freedom. Fieller's theorem states thathas a t-distribution with ν degrees of freedom.