Describe what probability proportional to size sampling is and why it is used. (b) At a nursery there are 10 plots, plot i has M; seedlings for a total of 800 seedlings: Primary sampling cluster (plot) 1 M 2 3 4 5 6 7 8 9 10 56 82 73 144 90 80 58 69 104 44 A sample of 5 plots should be drawn (without replacement) with probability proportional to M. Use the cumulative-size method to determine which plots should be included in the sample. Use the following numbers obtained from a random number table: 67515 75107 61196 09385 83552 83744 (6) (c) Suppose that we sample 4 plots to obtain the total number of a certain subspecies of the seedlings in plot i with the following data: Plot 1 4 7 10 Number of subspecies 27 69 17 30 Estimate the population total of the subspecies and the standard error of this estimate. (6)