Description of non-precision in experimental field scores

Visual assessments are usually carried out on crop experimental plots with different treatments in order to determine the level of some factor, such a s disease or pest infestation and damage, which are scored for incidence or severity using a pre-determined range of scores. Real data collected in the form of scores on experimental fields are usuall y non-precise. This non-precision may be due to the scorer's inconsistency and judgmental error. It may also be due to the apparent interdependency of the scores, since a scorer will naturally compare the score of previous pl ots in order to determine the score of the present plot. Small differences in the "true" scores are concealed, especially when the scores' range is sm all, leading to further non-precision. Given a set of n scores in the order of observation, s(1), s(2),...., s(n), different methods for quantifying the nonprecision in score si are propose d. Data from a set of real scores from an entomological investigation are used to illustrate the proposed description of non-precision.