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Few studies have examined base rates of suboptimal effort among healthy, undergraduate students recruited for neuropsychological research. An and colleagues (2012, Conducting research with non-clinical healthy undergraduates: Does effort play a role in neuropsychological test performance? Archives of Clinical Neuropsychology, 27, 849-857) reported high rates of performance invalidity (30.8%-55.6%), calling into question the validity of findings generated from samples of college students. In contrast, subsequent studies have reported much lower base rates ranging from 2.6% to 12%. The present study replicated and extended previous work by examining the performance of 108 healthy undergraduates on the Dot Counting Test, Victoria Symptom Validity Test, Word Memory Test, and a brief battery of neuropsychological measures. During initial testing, 8.3% of the sample scored below cutoffs on at least one Performance Validity Test, while 3.7% were classified as invalid at Time 2 (M interval = 34.4 days). The present findings add to a growing number of studies that suggest performance invalidity base rates in samples of non-clinical, healthy college students are much lower than An and colleagues initial findings. Although suboptimal effort is much less problematic than suggested by An and colleagues, recent reports as high as 12% indicate including measures of effort may be of value when using college students as participants. Methodological issues and recommendations for future research are presented., (© The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

With the presumption that a shifted Maxwellian velocity distribution adequately describes the electrons in a flowing plasma, a method with optimum signal to noise resolution to measure directed velocity is described. The lowest velocity that can be determined by this method is shown to depend on the electron random thermal velocity. The basic diagnostic system is outlined and consists of a ruby laser source and two detectors set 180 degrees from each other and both set at 90 degrees with respect to the incident laser beam. Simplified analysis compared to standard peak shift detection techniques is seen to be possible using optimization techniques. This proposed method is shown to be superior in SNR for plasma temperature below 7.2 eV.

Conventional Thomson scattering using a ruby laser evidences difficulty in scattered signal detection for electron densities < 10(13) cm(-3). Use of a Nd-glass laser source in combination with appropriate detectors can result in gains in the resolution of scattered signal of at least 1 order of magnitude over a conventional ruby laser system. However, due to the ~2.5-nm full bandwidth of a Nd-glass laser line, the electron temperature information in the incoherent scattered signal must be extracted from a Voigt profile, not from the usual Gaussian profile as when a ruby laser is used.