Two-phase sampling in estimation of population mean in the presence of   non-response
  The present paper presents the detail discussion on estimation of population mean in simple random sampling in the presence of non-response. Motivated by Gupta and Shabbir (2008), we have suggested the class of estimators of population mean using an auxiliary variable under non-response. A theoretical study is carried out using two-phase sampling scheme when the population mean of auxiliary variable is not known. An empirical study has also been done in the support of theoretical results. 
Manoj Kr. Chaudhary, Anil Prajapati, Rajesh Singh and Florentin   Smarandache
math.ST stat.TH