Relative costs and statistical power in the extreme groups approach

The relationship between variables in applied and experimental research is often investigated by the use of extreme (i.e., upper and lower) groups. Recent analytical work has provided an extreme groups procedure that is more powerful than the standard correlational approach for all values of the correlation and extreme group size. The present article provides procedures to optimize power by determining the relative number of subjects to use in each of two stages of data collection given a fixed testing budget.The opinions or assertions contained herein are those of the writers and are not to be construed as official or reflecting the views of the Navy Department.Edward F. Alf, Jr. is also affiliated with the Department of Psychology, San Diego State University.     

Do the mentally retarded have poor memory?

The hypothesis that mentally retarded persons have a short-term memory deficit whixh is due to inadequate rehearsal strategies is reexamined. A reevaluation of results of a number of experiments suggests that normal and retarded persons differ on short-term memory tasks, and the superiority of normals is present from the time of initial stimulus exposure. While some evidence for slope differences in retention curves is found in a few tasks, it is not strong support for memory differences. The hypothesis that “memory” differences are due to differential encoding as a result of more adequate rehearsal by the normal subjects is unacceptable. If this were the case, some differences in slope of retention curves could be expected unless rehearsal beyond the encoding stage was totally precluded. The review points to a need for an empirical reevaluation of the issue with a full recognition that deficits in particular processes may characterize some retarded persons and not others.     

Alcohol breath tests: Criterion times for avoiding contamination by “mouth alcohol”

Using either a gas chromatography or an infrared absorption technique, series of blood alcohol concentrations (BACs) determined by breath tests were obtained from human subjects immediately subsequent to their having only oral contact with beverages ranging in ethyl alcohol concentration from 4% to 95% +. Times for total dissipation of mouth alcohol residuals to a level of practical nonsignificance ranged from 10 to 19 min. Dissipation rates were an inverse and approximately exponential function of the ethyl alcohol concentration of the beverage and were greatly shortened by rinsing the mouth with warm (34°C) water prior to testing. The results are discussed in terms of their relevance to the methodology of a number of research studies employing BAC breath-testing equipment.     

The effects of a response cost treatment tactic on hyperactive children

In a pilot study, a multielement design was used to assess the effectiveness of a response cost procedure on a 7-year-old child's hyperactive behavior and academic performance across days. The procedure was effective in reducing off-task behavior and in increasing academic assignment completion. In Experiment 2, three strategies were compared to a no-treatment baseline in treating an 8-year-old hyperactive child: drug (Ritalin) alone, response cost alone, and drug plus response cost. The cost program alone and the cost program combined with medication were effective in reducing off-task behavior and in increasing academic performance. In both studies, the procedure was viewed by the teachers as practical and effective for use in a classroom setting. The subjects liked the cost system and believed that they completed more academic work when it was operative.     

Children's detection and awareness of textual anomaly

Children of 8 and 11 years were assessed in two experiments for their sensitivity to textual anomaly. In Experiment 1, subjects read stories containing two target lines, one appropriate and the other anomalous in relation to previously given information. Both age groups read the anomalous line more slowly than the appropriate line, but in a subsequent test of comprehension monitoring, the older group was more likely than the younger group to pick out the anomalous line as not fitting in with the rest of the story. Experiment 2 produced similar results: both 8- and 11-year-old children read an anomalous line more slowly, but 11-year-olds were more likely than 8-year-olds to cite the anomalous line or part of it when questioned about the possible presence of a line that did not fit in with the rest of the story. The results indicate that an age change in comprehension monitoring as indexed by citation or selection of a textual anomaly need not be contingent upon a parallel age change in constructive processing as indexed by modulation of reading rate.     

Two subjective scales of number

The way in which the apparent magnitude of numbers grows with their absolute magnitude was measured with a modified version of the direct technique Marks and Slawson (1966) used to determine the psychophysical exponent for loudness. This modified technique required subjects to estimate how evenly and randomly a sequence of integers appeared to sample the numerical continuum. The results indicate that the apparent magnitude of numbers increases with a decelerated power function of their arithmetic magnitude when a series samples from an open-ended range. However, when an upper boundary of the range is specified, the subjective scale seems to be linear. Random productions of numbers parallel the results found with judgments of presented sequences. The two scales of number provide the basis for an interpretation of the difference between magnitude and category scales: that subjects use numbers differently when the response scale is open-ended Imagnitude estimation than when it has a fixed upper limit tcategory scale. Given the assumption that subjects use numbers in this way in the two tasks, the qualitative relation between magnitude and category scales is predicted.     

Environmental control and the perception of control

The perception of control may be established if an individual is provided with an opportunity to choose and if the outcome of the choice is moderately uncertain. In turn, perceived control has been shown to enhance motivation and performance. In the present experiment, the effects of uncertainty about environmental control were examined by measuring the speed with which choices were made. When control was implicitly provided, decision latencies were shorter than when control was either explicitly available or not available at all. Paradoxically, providing information about control may reduce uncertainty and thereby diminish the perception of control. The contribution of control and choice to the development of perceived control is discussed.This research is based on a thesis by the first author submitted in partial fulfillment of the master of science degree at Virginia Polytechnic Institute and State University and was supported by a grant from the U.S. Army Research Office to the second author.