Analysis of downy mildew data on field pea: an empirical comparison of two logistic models |
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| Authors: | Ewa Bakinowska Wieslaw Pilarczyk |
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| Institution: | 1. Department of Mathematical and Statistical Methods, Poznan University of Life Sciences, Wojska Polskiego 28, Poznan 60-637, Poland;2. The Research Centre for Cultivar Testing, Slupia Wielka 63-022, Poland |
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| Abstract: | In the years 2002–2005, special trials concerning the level of infection of pea varieties by downy mildew were performed in Poland. In these trials, the large number of varieties were tested in many locations (environments), separately on reach and light soils. Obtained trial data are unique because of the large scale of the performed investigations and also for the fact that all the observations were made by the same observer. In a paper, two methods of statistical analysis of such (ordered) data are compared. Several models have been proposed for the statistical interpretation of ordinal data. One of the most popular is the cumulative-type fixed logistic model. In the present work, using two field pea data sets, we considered whether adding random effects to the simple logistic model can improve inference. It was investigated whether there is any difference between the decisions concerning varieties resulting from the simple logistic model and the proposed mixed logistic model. The two models were also compared in terms of goodness of fit. According to two applied goodness-of-fit statistics, the mixed model performed better in all the cases. Statistical analysis (what is important for practical agriculture) enabled identification of the most resistant and the most susceptible variety from the analyzed set of cultivars. |
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| Keywords: | categorical data goodness of fit infection logistic models multi-environment trials |
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