Let f(q) be the density function of the threshold variable qt, and denote γτ = γ0 + γ1 sin(2πkτ) + γ2 cos(2πkτ), Dτ = D(γτ0), Vτ = V(γτ0) and fτ = f(γτ0), where γτ0 is the true value of γτ as γτ0 = γ00 + γ10 sin(2πk0τ) + γ20 cos(2πk0τ), in which γ00, γ10, γ20, and k0 are the true values of γ0, γ1, γ2, and k, respectively.