INTERPRETATION AND USE OF NATIONAL TURFGRASS EVALUATION PROGRAM DATA
The National Turfgrass Evaluation Program (NTEP) encourages the proper and ethical use of its data. Data should not be referenced out of context, nor should a cultivar’s performance be elevated beyond supporting NTEP data.
Users of this data (in advertising) are encouraged to utilize complete tables, excluding only experimental lines not commercially available. If only part of a table is used, the top and bottom cultivars should be listed and reference should be made to the fact that the entire table is available on request. Tables should always reference the LSD value, the test location, the year the test was established, the date(s) of data represented and indicate whether the data are means of 1-month, 1-year or several years.
Readers and users of this data should be aware that cultivar differences are based on use of Least Significant Difference (LSD) statistics for mean separation. The LSD value(s) is located at the bottom of each table. To determine whether a cultivar’s performance is truly different from another, subtract one entry’s mean from another entry’s mean. If this value is larger than the LSD value, the observed difference in cultivar performance is significant and did not happen by chance. For example, two cultivars, “X” and “Y”, have mean turfgrass quality values of 7.0 and 5.0, respectively, with the LSD value being 1.0. Since the difference between “X” and “Y” (2.0) is larger than the LSD value (1.0), cultivar “X” performed significantly better than cultivar “Y” for mean turfgrass quality. Please remember that results can vary from year to year and from location to location. Therefore, always reference the LSD value when interpreting test results.
NTEP data is evaluated under the statistical procedure known as Additive Main Effect and Multiple Interaction (AMMI). AMMI identifies the genotypes (or turfgrass entries in this case) and how they interact with each environment (trial location), captures true structure in those interactions (in a data form), and improves the accuracy of the statistical analysis. This is done due to the large variety of environments NTEP works with.
If you feel NTEP data has been used improperly, please send the information to National Turfgrass Evaluation Program, BARC-West, Bldg. 002, Room 013, Beltsville, Maryland 20705.
For more information on NTEP, please visit http://www.ntep.org/