S138 Chapter 4

• Auxiliary Variable - a variable whose value is known in the population and which is highly correlated with the variable of interest
• Ratio estimation is the most appropriate

  • If a straight line passes through the origin
  • If the variance of $y_i$ about the line sis proportional to $x_i$
• Poststratification

  • Little information
• When the sample size in each stratum is small, the combined ratio estimator is better
• When the ratios vary greatly from stratum to stratum, the separate ratio estimator is better