A forester wants to estimate the total number of trees on a tree farm that have a diameter exceeding 12 inches. Because the farm contains too many trees to facilitate measuring all of them, she uses Google Earth to divide the farm into 250 rectangular plots of approximately the same area. An examination of the plots reveals that 27 of the plots have a sizable portion of their land under water. The forester excluded the 27 “watery” plots for the study. She then randomly selected 42 of the remaining 223 plots and counted all the trees having a diameter exceeding 12 inches on the 42 selected plots.
a. What is the sampling frame for this study?
b. How does the sampling frame differ from the population of interest, if at all?
c. What biases may exist in the estimate of the number of trees having a diameter greater than 12 inches based on the collected data?