Statistical Sampling – Important Update
Thanks to all of our Inspecting Foresters who made the 2006 sampling implementation year possible! As you know, ATFS is moving to a system of statistical sampling to ease the burden on State Tree Farm Committees and make Tree Farm a more credible and efficient certification system. Don’t forget, your state still has the option to complete all of the 5 year reinspections after completing the required sample inspections.
In 2006, we heard from many inspectors and State Committee volunteers about the unusual number of large properties that were selected as part of the sample. Because of these observations, we went back to Virginia Tech to inquire about the discrepancy. We learned that the sample was run on a Probability Proportionate to Size sample formula which made our larger properties more likely to be selected in the sample. While this is an efficient way to sample the most acres overall, it will not be sustainable year after year.
In 2007, ATFS will use a Stratified Random Sample, grouped by acre classes across the nation to choose the sample. This will eliminate the bias toward large properties. All certified properties will be eligible, and remember, there is no longer a Member category! Virginia Tech has made the last changes to the formulas and they are currently running the numbers for the 2007 sample.
It’s important to note that under a sampling strategy, properties visited this year or last year are still eligible for next year’s sample. While there is only a slight chance that these properties will be selected two years in a row, it is a possibility. It is still important to complete these inspections to maintain the credibility and integrity of our national sample. Thanks again for your help in making sampling happen.
