VARIANCE AS A FACTOR EFFECT IN INTERDISCIPLINARY STUDIES OF AGRICULTURAL SYSTEMS

Studies of interrelationships among factors typically focus on factor effects related to the mean response. In some instances, response variances, as well as, or even rather than, response means, may be affected by the factors under consideration. In this paper, generalizations of Levene\u27s test and the Jackknife test to two-factor experimental designs are studied via simulation studies to assess their ability to identify differences in the variance as an interaction effect or as a factor main effect. These tests are then applied to a particular example where relationships between chile plants and two prominent pests of chile plants -nematodes and yellow nutsedge -- are under study. This example illustrates the utility of these tests in studying relationships among factors in agricultural systems

DATA STRUCTURE WITH RESPECT TO THE MAIN EFFECTS MODEL: A DISCUSSION MOTIVATED BY A META-ANALYSIS DATA SET

A discussion on data structure relative to the main effects model is motivated by a severely unbalanced meta-analysis data set. This data set is used to highlight the difficulty of assessing data structure when multiple factor data sets are severely unbalanced. Both theoretical results and numerical examples are used to establish that simple approaches to examining data structure using two-way tables provide easily assimilated information about the effect of data unbalance on main effect contrast variances. In addition, notions of balance, proportionality, unbalance, and missing cells with respect to the main effects model are defined in terms of the two-way tables and are related to main effect contrast estimate variances as assessed using the D-optimality criterion

Comparison of Some Approaches to Determine Spatial Dependence of Soil Properties

Knowledge of variability and spatial structure of soil properties is essential for optimal design for collecting soil samples and effectively applying management decisions in the field. The objective of this study is to compare some approaches for characterizing, and comparing spatial dependence of isotropic second-order stationary processes. The evaluated approaches are the nugget to sill ratio (NR), normalized (by fitted sill) semivariogram, correlograms, and two integral scales. Soil samples, collected at a regular 50 m × 50 m grid from 0-15 cm depths, were analyzed for sand and clay, bulk density (b), saturated hydraulic conductivity (Ks), wilting point, available water content (AWC), pH, electrical conductivity (EC), nitrate-nitrogen (NO3- N), and chloride (Cl) were determined. Geostatistical software (GS+, Gamma Design Software, Plainwell, MI) was used to estimate the variance structure of various measured soil properties. Analysis include using data on the spatial variability of various properties from four published studies. NR displayed spatial dependence ignoring the influence of range, normalized semivariogram and correlogram provided the visual comparison, and both integral scales incorporated the influence of range and provided single number spatial dependence summaries. Either of the integral scale formulations can be used to characterize the spatial dependence of soil properties from agricultural fields

Journal of Technology Education

Published versio

Inclusion in Rural and Urban Classrooms in New Mexico

The New Mexico Department of Education has recommended that New Mexico schools work toward full inclusion in the classroom. All students regardless of disabilities will be included in the regular classroom to the maximum extent possible. The authors of this article address current inclusion practices in special education. The legislature, professional educators, and parent support groups are continually working to develop better methods for teaching students with disabilities. Special education is currently undergoing major changes related to the least restrictive educational placement. At the forefront of educating students with disabilities is the full inclusion model of education. Proponents and opponents are divided regarding this controversial paradigm. The authors conducted a modified Delphi Survey and examined the pros and cons of full inclusion in one urban and two rural New Mexico communities. Educators responded to a survey instrument concerning the perceived benefits and problems of inclusion in their rural school districts. </jats:p