Chakrabarty (1979), Khoshnevisan et al. (2007),  Sahai and Ray  (1980),  Ismail et al. (2011) and Solanki et al. (2012) proposed estimators for estimating population mean Y.  Up to the first order of approximation and under optimum conditions, the minimum mean squared error (MSE) of all the above estimators is equal to the MSE of the regression estimator.