Testing for heterogeneity of experimental error for combined analysis
1996
Chantana Sorasiri | Puttana Roongravee | Manat Pithuncharurnlap (Department of Agriculture, Bangkok (Thailand). Planning and Technical Div.)
For experiments conducted at several sites or repeated several seasons, the purpose is to obtain information of the interaction of environment and treatment to increase the scope of inference. Before using a combined analysis over sites or seasons the homogeneity of error variance must be examined. In practice, the error variances can be considered homogeneous if the highest error mean square is not three-fold larger than the smallest error mean square where it is referred to as the three-fold procedure. However, the result that obtained by this procedure often differ from that obtained by the Bartlett's test. Therefore, a Cochran's test is considered as an alternative procedure. To investigate the efficiency of the three-fold and the Cochran's procedure, the results of testing the homogeneity of error variance that obtained between the two procedure are compared considering the Bartlett's test as the standard procedure. The 102 sets of data with 3 more than 3 sites from the rice research project of rice variety trials for irrigated area, 1986-93 were used. The results indicated that the Cocharan's test gave 87 percent of the time for getting the same results as Bartlett's test, while the three-fold procedure gave 51 percent of the time. It was therefore recommended that the Cochran's test was more efficient in testing the homogeneity of error variance than the three-fold procedure.
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