Monitoring Field Variability Using Confidence Interval for Coefficient of Variation

The construction of an exact confidence interval (CI) for a single coefficient of variation (CV) is computationally cumbersome, but a number of approximation methods exist. The existing methods of CI construction are not appropriate for the agricultural experiments involving a single crop grown over several locations. There is a need to assess and identify an appropriate approximate method from the existing methods, and provide a new approach for multiple experiments. Simulation and real data were used in the evaluation process. The Vangel (1996 Vangel , M. G. ( 1996 ). Confidence intervals for a normal coefficient of variation . Am. Statist. 50 : 21 – 26 .[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) approximation method was computationally easier and produced an approximate length of CI close to that obtained by the exact method. For multiple experiments, the bootstrapping method performed better than other methods in the construction of CIs. Expected lower and upper confidence limits for coefficient of variation for various crop types were established using data from 513 trials conducted in Ethiopia. These CIs are used to monitor variability of new trials conducted on same locations.