P E Levy | PubMed Health

PubMed2000

Performance appraisal reactions: measurement, modeling, and method bias.

In this study, the authors attempted to comprehensively examine the measurement of performance appraisal reactions. They first investigated how well the reaction scales, representative of those used in the field, measured their substantive constructs. A confirmatory factor analysis indicated that these scales did a favorable job of measuring appraisal reactions, with a few concerns. The authors also found that the data fit a higher order appraisal reactions model. In contrast, a nested model where the reaction constructs were operationalized as one general factor did not adequately fit the data. Finally, the authors tested the notion that self-report data are affectively driven for the specific case of appraisal reactions, using the techniques delineated by L. J. Williams, M. B. Gavin, and M. L. Williams (1996). Results indicated that neither positive nor negative affect presented method biases in the reaction measures, at either the measurement or construct levels.

Adult↗

PubMed2000

Testing a process-based model of tree seedling growth by manipulating.

A model was developed that simulated photosynthesis, growth and allocation in tree seedlings. The model was parameterized with data from experiments on seedlings of sycamore (Acer pseudoplatanus L.), Sitka spruce (Picea sitchensis (Bong) Carr.) and young birch trees (Betula pendula Roth.). In these experiments, CO2 concentration ([CO2]) and nutrient addition rate were varied. Parameters quantifying nutrient uptake, translocation and starch synthesis were fitted, based on data from control treatments. Elevated [CO2] and low-nutrient treatments were then used to test the predicted response of growth and allocation against observations. The model accurately predicted total seedling growth in the elevated [CO2] treatments. A response of growth to elevated [CO2] was seen in the birch and sycamore experiments, but not in the Sitka spruce, because of photosynthetic down-regulation. Predictions of allocation were reasonably accurate in the birch and Sitka spruce experiments, but were notably poorer in the sycamore experiments, possibly because of differences in sink strength between root and shoot. In the birch and sycamore experiments, little change in allocation with elevated [CO2] was observed or predicted. This was ascribed to the relative values of K(Tc) and K(Tn), the translocation coefficients that determine the sensitivity of allocation to carbon and nitrogen uptake rates, respectively. Growth and allocation in the low-nutrient treatments were poorly predicted by the model. In Sitka spruce, it was suspected that the photosynthetic parameters measured in August 1994 had been higher earlier in the season, before nutrients became depleted. In sycamore, the discrepancies were thought to relate to differences in sink strength between root and shoot that could not be described by the model.

Carbon Dioxide↗