type-II Errors Research Articles

Risk assessment for complex chemical exposure in aquatic systems: the problem of estimating interactive effects.

The traditional, but little used, way of assessing effects of the interaction between known chemicals is to use factorial experimental designs. Such designs allow one to test for less than additive (antagonistic) and greater than additive (synergistic) effects. Whilst synergism can be demonstrated in such experiments the concentrations at which synergistic effects occur are extremely high and are unlikely to occur in nature. Recently developed techniques allow one to measure directly the effects of combined stressors in the field. These biological effect techniques range from tests on individual organisms to tests on communities. At the biochemical level the tests can indicate that the organism has been exposed to certain groups of chemicals (for example cytochrome P-450 enzymes responding to PAHs or metallothioneins responding to heavy metals). At the community level of organisation there are highly sensitive statistical techniques that indicate clearly the combined effect of stressors. The effects of oil exploration and production on benthic communities in the North Sea can be linked to concentrations of chemicals. However, such relationships are correlative and do not necessarily indicate cause and effect. Experiments are needed to test the hypotheses generated concerning the interactive effects of chemicals on the benthic species. The statistical analyses do, however, show which species have been affected and their relative sensitivity to chemical and physical disturbances. Such species are preferable to the traditional "laboratory weeds" usually utilised. A strategy for risk assessment is needed that combines an experimental protocol for making predictions, from laboratory experiments, of likely effects to be found in the field. This should be combined with field monitoring that allows one to detect changes that were not predicted. At present most monitoring designs cannot adequately detect trends. This is due to concentration on Type-I statistical errors rather than properly considering Type-II errors. By concentrating on Type-II errors one can design monitoring programmes that are able to detect trends with a given degree of precision. There are also strong ethical grounds for a change to giving more emphasis to Type-II errors.

Type-II statistical errors in environmental science and the precautionary principle

Type-II statistical errors in environmental science and the precautionary principle

Effects of non-normality on the power function in a one-way random model

The effects of non-normality on type-I and type-II errors in a one-way random model are investigated for moderate departures from normality. It is found that the probabilities of both errors are more sensitive to the kurtosis of between group effects than that of within group effects.

Does the "Blindness" of Peer Review Influence Manuscript Selection Efficiency?

Although we find Blank's results compelling, it is difficult to draw solid conclusions from them. Perhaps this is what Ashenfelter meant when he referred to the ambiguous findings regarding the nature of any biases. The issue of scientific concern vis-a-vis type of review process employed by journal editors is the severity of type-I and type-II errors. Do editors employing a single-blind review process systematically publish more papers that have little or no impact on the profession and/or fail to publish more truly good papers than do editors of double-blind journals? Blank's findings do not provide certain relevant information with respect to the type-I/typeII error problem that arguably plagues single-blind reviewing but not double-blind reviewing.

IRRIGATION, WATER RELATIONS, AND CRABAPPLE GROWTH IN ROOT-CONTROL BAGS IN A FIELD NURSERY

Limited root development of nursery stock in root-control bags facilitates harvest but without irrigation may predispose stock to water stress. The effect of bags and irrigation on growth and water relations of field-grown Malus sieboldii var. zumi were investigated following transplanting as large liners into a silty-clay soil. Predawn leaf water potential (ψ), and midday stomatal conductance (gs) and ψ, were measured periodically through the season. Late-season osmotic potential (ψπ), caliper, leaf area, and root growth were also measured. Non-irrigated treatments exhibited water stress during an extended mid-summer drought, as predawn ψ and particularly gs were less than irrigated treatments, resulting in lower vegetative growth and ψπ. For combined bagged treatments water relations did not differ, but leaf area, root growth, and ψπ, but not caliper, were less than non-bagged trees. Growth measurements and ψπ of non-irrigated bagged trees, however, were consistently lower but nonsignificant than the other treatments. Bag-induced root reduction can limit some top growth even with optimum soil water. Moreover, in terms of potential Type-II errors extrapolated over a conventional production cycle, trees grown in root-control bags in normally non-irrigated soils may be more susceptible to water stress and subjected to further cumulative growth limitation.

Enforcement Costs and the Optimal Magnitude and Probability of Fines

WHENEVER the government uses fines to control harmful activities, it incurs certain costs in connection with the enforcement process. This article will show how these costs affect the optimal magnitude of fines and the optimal degree of enforcement effort-that is, the optimal probability of detection of those who commit harmful acts. We will distinguish between two types of enforcement costs. Fixed enforcement costs are costs that do not depend on the number of individuals who commit harmful acts. These costs would include, for example, the expenses borne by a pollution control agency in testing water quality in a lake. Variable enforcement costs are costs that do depend on the number of individuals who commit harmful acts, such as the costs of prosecuting and penalizing polluters. In our basic model, we assume that the fixed enforcement costs are the costs of maintaining the probability of detection at a certain level and that the variable enforcement costs are the costs of fining individuals. The main conclusions of this article may be summarized as follows. The optimalfine equals the harm, properly inflatedfor the chance of not being detected, plus the variable enforcement cost of imposing the fine. If the fine is of this magnitude, the expected fine will equal the harm caused by the harmful act plus the expected increase in enforcement costs occasioned by it. For instance, suppose that the probability of detecting a

Variations in the proportion of abnormal cells and required sample sizes for human cytogenetic studies

A study of cytogenetic aberration rates in human beings was conducted (1) to determine the magnitude of variation in one index of aberration, that of the proportion of abnormal cells, and (2) to estimate the number of subjects and the number of cells per subject needed to detect significant increases of predetermined size over a control value with a type I error of α = 0.05 and typeII errors of β = 0.20 or 0.10. The index of interest, the proportion of abnormal cells, was defined as the ratio of cells with at least one aberration to all cells scored. The study subjects were 239 persons seen for preemployment evaluation at a division of a large U.S. chemical company. 200 cells were scored on each subject. The proportion of abnormal cells for this groups was 0.022. The variance among subjects was found to be significantly larger than the variance with subjects ( p < 0.001). Several combinations of sample size requirements were calculated for the purpose of determining the most reasonable number of subjects per group and cells per subject. The detection of relatively small increases over a control value requires either more subjects or more cells per subject, and from the point of view of the costs associated with the scoring of cells, greater savings will be accomplished in most cases by increasing the number of subjects, rather than increasing only the number of cells per subject.