Exponential ratio-product type estimators under second order   approximation in stratified random sampling
  Singh et al (20009) introduced a family of exponential ratio and product type estimators in stratified random sampling. Under stratified random sampling without replacement scheme, the expressions of bias and mean square error (MSE) of Singh et al (2009) and some other estimators, up to the first- and second-order approximations are derived. Also, the theoretical findings are supported by a numerical example. 
Rajesh Singh, Prayas Sharma and Florentin Smarandache
math.ST stat.TH