64-6 How Many Samples to Take: Power Analysis Applications to Soil Measurements.



Monday, October 17, 2011: 3:45 PM
Henry Gonzalez Convention Center, Room 209, Concourse Level

Alexandra Kravchenko, Crop and Soil Sciences, Michigan Stats University, East Lansing, MI
Soil carbon measurements are often highly variable, which makes the detection of statistically significant differences among different land uses and management systems difficult. A common mistake is to interpret a lack of statistical significance as evidence for the absence of differences. Ad-hoc power analysis is what should be used prior to conducting a field experiment or collecting soil samples in order to ensure high power of the statistical tests. Post-hoc power analysis should be used after the data are collected and analyzed if the results of statistical tests turn out to be not significant. I will present results of simulated and actual soil carbon measurements exploring effects of variability on sample/sub-sample requirements of the experimental studies that have monitoring soil carbon as one of their objectives.
See more from this Division: ASA Section: Biometry and Statistical Computing
See more from this Session: Symposium--Partnering Soil Science and Statistics, Ways to Avoid Statistical Malpractice In Soil Research: I