Estimation of genotypic effects for qualitative characters
1984
Urfer, W. (Dortmund Univ. (Germany). Dept. of Statistics)
In plant breeding and variety trials scores are widely used for the evaluation of semi-quantitative traits such as pest infestation. Observations of this type do not satisfy the usual assumptions of homoscedasticity and normal distribution of residuals. Therefore a threshold model is discussed for ordinal response variables. In this model it is assumed that the character under study depends on an unobservable continuous variable with different thresholds which generate discontinuity in the visible trait. For the maximum likelihood estimation of the parameters of the threshold model FISHER's scoring method was used. As an illustration an experiment with 31 varieties of rape at 9 locations is analyzed, using the information on the infection by the fungus Phoma lingam.
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