The component of technical efficiency change can be further decomposed into pure technical efficiency change and scale efficiency change. Assuming the variable returns to scale technologies TVRSt and TVRSt+1 for the two-time periods τ = {t, t+1}, i.e. TVRSτ={(xτ,yτ): ∑j=1nλjτxj,iτ≤xiτ , i=1,2,…m,∑j=1nλjτyj,rτ≥yrτ ,r=1,2,…,s,∑j=1nλjτ=1,λjτ≥0, j=1,2,…,n}, and the corresponding distance functions dVRSτ(xφ,yφ)=max{θ>0:(xφ/θ,yφ) ∈ TVRSτ}, where τ = {t, t +1} and φ = {t, t +1}