Monitoring Field Variability Using Confidence Interval for Coefficient of Variation

Abstract

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) 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.

Designing a multiple dependent state sampling plan based on the coefficient of variation

“…Steel and Torrie ( 1980 ), Taye and Njuho ( 2008 ) point that the CV is a good measure of the reliability of the experiment. Here we use the CV as the quality benchmark for acceptance of a product lot.…”

“…CV is a good measure of the reliability of experiments, that is, the smaller the CV value, the higher the reliability (Steel and Torrie 1980 ; Taye and Njuho 2008 ). Recently, Ma and Zhang ( 1997 ) deduced the CV method for structural reliability inspection using the CV as the quality control parameter, under the condition of the CV being known.…”

Design of a Quick Switching Sampling System Based on the Coefficient of Variation

“…For such a case, the CV can be regarded as a suitable quality index to evaluate the stability of the product quality. In manufacturing industries, the CV has been widely used in many practical applications of quality control, such as reliability [16][17][18], control chart [15,19,20] and acceptance sampling plan. [21][22][23][24] By exploring the literature and utilizing the best of the authors' knowledge, the existing sampling plans based on CV include the single sampling plan [21,22], the multiple dependent state sampling plan [23] and the two-stage sampling plan [24].…”

An examination of the variability of agricultural production using a new approximate confidence interval for the coefficient of variation

“…Hence the researcher should use it carefully. One way is to use the confidence intervals for the coefficient of variation by considering the width of the range that is indicative of an environment suitable for agricultural production, such as the variability of agricultural production by the confidence intervals for coefficient of variation 2 . This article examines and compares different methods.…”