 ለትክክለኛ ተለዋዋጭ ተፅእኖዎች, Deaton (2010) እና ተለዋዋጭ መለኪያዎች በንፋስ መሳሪያዎች (ዝናብ መሳሪያ ነው) ለማግኘት, Murray (2006) ይመልከቱ.
Kwa maganizo kukayikira zosintha zoimbidwa kuona Deaton (2010), ndi chiyambi zosintha zoimbidwa ndi zida ofooka (mvula ndi chida ofooka), onani Murray (2006).