Skip to page content
USDA Forest Service
  
Treesearch

Research & Development Treesearch

 
Treesearch Home
About Treesearch
Contact Us
Research & Development
Forest Products Lab
International Institute of Tropical Forestry
Northern
Pacific Northwest
Pacific Southwest
Rocky Mountain
Southern
Help
 

GeoTreesearch


Science.gov - We Participate


USA.gov  Government Made Easy


Global Forest Information Service

US Forest Service
P.O. Box 96090
Washington, D.C.
20090-6090

(202) 205-8333

You are here: Home / Search / Publication Information
Bookmark and Share

Publication Information

(249 KB bytes)

Title: Sample-size needs for forestry herbicide trials

Author: Zedaker, S.M.; Gregoire, T.G.; Miller, James H.

Date: 1994

Source: Canadian Journal of Forest Research, 23(10): 2153-2158.

Publication Series: Not categorized

Description: Forest herbicide experiments are increasingly being designed to evaluate smaller treatment differences when comparing existing effective treatments, tank mix ratios, surfactants, and new low-rate products. The ability to detect small differences in efficacy is dependent upon the relationship among sample size. type I and II error probabilities, and the coefficients of variation of the efficacy data The common sources of variation in efficacy measurements and design considerations for controlling variation ate reviewed, while current shortcomings are clarified. A summary of selected trials estimates that coefficients of variation often range between 25 and 100%, making the number of observations necessary to detect small differences very large, especially when the power of the test (1 - ß) is considered. Very often the power of the test has been ignored when designing experiments because of the difficulty in calculating ß. An available program for microcomputers is introduced that allows researchers to examine relationships among sample size, effect size, and coefftcients of variation for specified designs, a and ß. This program should aid investigators in planning studies that optimize experimental power to detect anticipated effect sizes within resource constraints.

Publication Notes:

  • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

XML: View XML

Citation:


Zedaker, S.M.; Gregoire, T.G.; Miller, James H. 1994. Sample-size needs for forestry herbicide trials. Canadian Journal of Forest Research, 23(10): 2153-2158.

 


 [ Get Acrobat ]  Get the latest version of the Adobe Acrobat reader or Acrobat Reader for Windows with Search and Accessibility

USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.