关于数量化I方法的自变量之间交互作用计算

自变量之间存在交互作用时,在应用数量化方法Ｉ时如何计算自变量间的交互作用建立数量化方程．     

Distribution of plant functional attributes in a managed forest in relation to neighbourhood structure

The importance of neighbourhood structure on the distribution of plant functional attributes was investigated in two managed forests in Denmark. Species composition was recorded for 325 plots of 5×5 m and species were assigned to functional groups based on vegetative attributes: (a) Raunkiaer life-form and (b) height of adult plants, and regenerative attributes: (c) mode of dispersal and (d) pollination class. The distribution of attributes was related to neighbourhood parameters that reflect the composition, distribution and diversity of nine habitat classes within a 25-m radius from the focal plot. Regression trees were used to analyse counts of attributes per plot. Best predictors were neighbourhood scores for open areas, road-side habitat, and neighbourhood diversity. The correlation between individual functional attributes and neighbourhood parameters were presented in a correlation matrix. A cluster analysis, representing a first step towards the construction of plant functional types, resulted in five groups characterised by a particular combination of functional attributes and preference of neighbourhood.     

The estimation of adult stature from metacarpal bone length

Stature was measured (in cm) in 166 (120 male; 46 female) predominantly white adults (age range: 17–87 years). A radiograph of one hand of each subject was taken (for routine diagnostic purposes) and the inter-articular length of all five metacarpal bones was measured with a sliding caliper. These metacarpal lengths were then adjusted to compensate for enlargement during radiography. A significant correlation coefficient between stature and metacarpal length was observed in both sexes. Regression equations were computed from the length of each metacarpal, by which living stature may be fairly accurately estimated in the absence of any complete limb bones. The difference between our estimates and those obtained by more orthodox methods is usually less than 3%.     

Assessing broomrape risk due to weeds in cropping systems with an indicator linked to a simulation model

Integrated crop protection tolerates residual weed floras if they are not harmful for crop production. These weeds can host harmful crop pests, among which parasitic plants such as branched broomrape (Phelipanche ramosa). This holoparasite is responsible for large yield losses in French crops such as oilseed rape. To date, there are no herbicides available to control it. To evaluate ex ante the impact of crop management practices on weed-mediated parasite infection of crops, we developed an indicator calculated from outputs of the weed dynamics model FlorSys. It consists of three components assessing weed impact on (1) stimulation of parasite germination during the whole cropping season, i.e. the potential risk reduction for future crops via a reduction of the parasite seed bank, (2) the stimulation of parasite germination in host crops, i.e. the potential risk increase for the current crop, (3) parasite reproduction on weed plants, i.e. the potential risk increase for future crops. This indicator was then used to predict weed-mediated broomrape risk in cropping systems from six regions from France and one from Spain. Antagonisms and synergies with other indicators of weed-harmfulness for crop production and weed contribution to plant and functional biodiversity were investigated with Pearson correlation analyses. For instance, cropping systems with a high parasite risk also had a high functional biodiversity (e.g. weed-based food offer for bees). Effects of crop management practices on the weed-mediated parasite risk indicator were identified with linear models; regression trees were used to identify the combinations of management practices that maximised or minimised weed-mediated broomrape risk. Parasite risk depended on crop rotation, sowing and harvest dates, tillage, herbicides and mechanical weeding. The lowest risk was observed in fields that were last tilled less than 21 days before sowing, with more than 0.6 herbicides per year (i.e. 3 applications in 5 years) with multiple entry modes into the weeds (e.g. leaves and roots) and the last herbicide sprayed no later than 127 days before harvest. RLQ analyses were used to identify correlations between weed species traits (Q matrix) and simulated parasite risk (R matrix), via simulated weed densities (L matrix). Early summer-emerging weed species increased parasite risk. No other notable correlations were found, indicating that parasite risk results from a weed community of interacting species, and not simply from individual weed species. An advice table was built to summarize and explain the effects of crop management practices on weed-mediated parasite risk.     

Mechanical biomarkers of medial compartment knee osteoarthritis diagnosis and severity grading: Discovery phase

ObjectiveTo investigate, as a discovery phase, if 3D knee kinematics assessment parameters can serve as mechanical biomarkers, more specifically as diagnostic biomarker and burden of disease biomarkers, as defined in the Burden of Disease, Investigative, Prognostic, Efficacy of Intervention and Diagnostic classification scheme for osteoarthritis (OA) (Altman et al., 1986). These biomarkers consist of a set of biomechanical parameters discerned from 3D knee kinematic patterns, namely, flexion/extension, abduction/adduction, and tibial internal/external rotation measurements, during gait recording.Methods100 medial compartment knee OA patients and 40 asymptomatic control subjects participated in this study. OA patients were categorized according to disease severity, by the Kellgren and Lawrence grading system. The proposed biomarkers were identified by incremental parameter selection in a regression tree of cross-sectional data. Biomarker effectiveness was evaluated by receiver operating characteristic curve analysis, namely, the area under the curve (AUC), sensitivity and specificity.ResultsDiagnostic biomarkers were defined by a set of 3 abduction/adduction kinematics parameters. The performance of these biomarkers reached 85% for the AUC, 80% for sensitivity and 90% for specificity; the likelihood ratio was 8%. Burden of disease biomarkers were defined by a 3-decision tree, with sets of kinematics parameters selected from all 3 movement planes.ConclusionThe results demonstrate, as part of a discovery phase, that sets of 3D knee kinematic parameters have the potential to serve as diagnostic and burden of disease biomarkers of medial compartment knee OA.     

Estimation of a Conditional Mean in a Linear Regression Model

Consider the two linear regression models of Y_ij on X_ij, namely Y_ij = β_io + β_il X_ij + ε_ij,j = 1,2,…,n_i, i = 1,2, where ε_ij are assumed to be normally distributed with zero mean and common unknown variance σ². The estimated value of a mean of Y₁ for a given value of X₁ is made to depend on a preliminary test of significance of the hypothesis β₁₁ = β₂₁. The bias and the mean square error of the estimator for the conditional mean of Y₁ are given. The relative efficiency of the estimator to the usual estimator is computed and is used to determine a proper choice of the significance level of the preliminary test.     

Do intrinsically dominant and subordinate species exist? A test statistic for field data

Abstract. We propose a new method to obtain information about processes that structure plant communities. We analysed the relationship between the presence and dominance of species across a range of habitats. A simple regression model was used to describe this relationship for each species. Based on the regression parameters, we distinguished globally dominant species, which dominate in the same proportion of plots within a habitat as in which they occur, locally dominant species, which reach dominance only when present in almost every plot of a habitat, and intrinsically subordinate species, which never attain dominance. We tested this method using a large data set of species occurrences across a range of salt marsh habitats. The relationships between presence and dominance could be described well by the regressions, and showed large differences between the species. Global dominants occurred later in the succession and higher on the elevational gradient than intrinsically subordinate species. Local dominants were characteristic of early successional stages. These patterns are discussed in the light of colonisation-competition and tolerance-competition trade-offs.     

田间大豆光合午休原因的综合研究

本研究利用主成分分析构造同归模型,利用典型相关分析等方法,对自变量的重要程度进行排序,确定了光合午休的主要原因是气孔因素限制所致.光抑光合也是一个值得注意的因素,但不是主要因素.空气相对湿度、叶片与大气间水汽压差是诱发气孔限制的重要因素.当空气相对湿度较为适中时,叶温的影响较小,在空气相对湿度变坏的情况下,叶温才对光合午休有重要影响.