Unbiased Ratio-Type Estimator Using Transformed Auxiliary Variable In   Negative Correlation Case
  The objective of this paper is to propose an unbiased ratio-type estimator for finite population mean when the variables are negatively correlated. Hartley and Ross[2] and Singh and Singh [6] estimators are identified as particular cases of the proposed unbiased estimator. The variance expression of the proposed estimator to the first degree of approximation has been obtained. An empirical study is carried out to demonstrate the performance of the proposed estimator over, Robson [5] estimator and Singh and Singh [6] estimator. 
Jayant Singh, Housila P. Singh, Rajesh Singh
stat.ME