Vacuum Electronics, International Conference, 2000
IOTs (inductive output tubes) are relatively novel vacuum electron devices that have established ... more IOTs (inductive output tubes) are relatively novel vacuum electron devices that have established their position as reliable and highly efficient UHF amplifiers, predominantly in the television transmitter service. In this application, they reach output power levels equivalent to about 50 kW CW. Scientific applications, like proton accelerators, require UHF amplifiers with considerably higher output power capability. Super power klystrons are
Psychological studies in general, and psy-chobiological studies in particular, routinely use a co... more Psychological studies in general, and psy-chobiological studies in particular, routinely use a collec-tion of classic statistical techniques aimed at comparing groups or studying associations. A fundamental issue is whether violating the basic assumptions underlying these methods, namely normality and homoscedasticity, can result in relatively poor power or miss important features of the data that have practical significance. In the statistics literature, hundreds of papers make it clear that under general conditions the answer is yes and that routinely used strategies for dealing with violations of assumptions can be unsatisfactory. Moreover, a vast ar-ray of new and improved techniques is now available for dealing with violations of assumptions, including more flexible methods for dealing with curvature. The pa-per reviews the major insights regarding standard meth-ods, explains why some seemingly reasonable methods for dealing with violations of assumptions are technically unsoun...
Angular impulse generation is dependent on the position of the total body center of mass (CoM) re... more Angular impulse generation is dependent on the position of the total body center of mass (CoM) relative to the ground reaction force (GRF) vector during contact with the environment. The purpose of this study was to determine how backward angular impulse was regulated during two forward translating tasks. Control of the relative angle between the CoM and the GRF was hypothesized to be mediated by altering trunk-leg coordination. Eight highly skilled athletes performed a series of standing reverse somersaults and reverse timers. Sagittal plane kinematics, GRF, and electromyograms of lower extremity muscles were acquired during the take-off phase of both tasks. The magnitude of the backward angular impulse generated during the push interval of both tasks was mediated by redirecting the GRF relative to the CoM. During the reverse timer, backward angular impulse generated during the early part of the take-off phase was negated by limiting backward trunk rotation and redirecting the GRF ...
When data are nonnormal in form classical procedures for assessing treatment group equality are p... more When data are nonnormal in form classical procedures for assessing treatment group equality are prone to distortions in rates of Type I error and power to detect effects. Replacing the usual means with trimmed means reduces rates of Type I error and increases sensitivity to detect effects. If data are skewed, say to the right, then it has been postulated that asymmetric trimming, to the right, should be better at controlling rates of Type I error and power to detect effects than symmetric trimming from both tails of the data distribution. Keselman, Wilcox, Othman and Fradette (2002) found that Babu, Padmanabhan and Puri's (1999) test for symmetry when combined with a heteroscedastic statistic which compared either symmetrically or asymmetrically determined means provided excellent Type I error control even when data were extremely heterogeneous and very nonnormal in form. In this paper, we present a detailed discussion of the Babu et al. procedure as well as a numerical example ...
Communications in Statistics - Simulation and Computation, 2014
ABSTRACT Simulation results are reported on methods that allow both within group and between grou... more ABSTRACT Simulation results are reported on methods that allow both within group and between group heteroscedasticity when testing the hypothesis that independent groups have identical regression parameters. The methods are based on a combination of extant techniques, but their finite-sample properties have not been studied. Included are results on the impact of removing all leverage points or just bad leverage points. The method used to identify leverage points can be important and can improve control over the Type I error probability. Results are illustrated using data from the Well Elderly II study.
Fifth IEEE International Vacuum Electronics Conference (IEEE Cat. No.04EX786), 2004
Summary form only given. Irrespective of the type RF device, the starting point for RF power prod... more Summary form only given. Irrespective of the type RF device, the starting point for RF power production is generation of a high quality electron beam. The quality of the electron beam is determined by the optical design of the gun and the quality of the cathode. Unfortunately, RF engineers have insufficient control of cathode quality. A vacuum test facility has
The Welch-James and Improved General Approximation tests were examined in between-subjects × with... more The Welch-James and Improved General Approximation tests were examined in between-subjects × within-subjects repeated measures designs for their rates of Type I error when data were nonnormal, nonspherical, and heterogeneous and when group sizes were unequal as well. The tests were computed with either least squares or robust estimators of central tendency and variability and assessed with critical values that
ABSTRACT The paper describes two new methods for comparing two independent, discrete distri¬butio... more ABSTRACT The paper describes two new methods for comparing two independent, discrete distri¬butions, when the sample space is small, using an extension of the Storer–Kim method for comparing independent binomials. These methods are relevant, for example, when compar¬ing groups based on a Likert scale, which was the motivation for the paper. In essence, the goal is to test the hypothesis that the cell probabilities associated with two independent multinomial distributions are equal. Both a global test and a multiple comparison procedure are proposed. The small-sample properties of both methods are compared to four other techniques via simulations: Cliff’s generalization of the Wilcoxon–Mann–Whitney test that effectively deals with heteroscedasticity and tied values, Yuen’s test based on trimmed means, Welch’s test and Student’s t test. For the simulations, data were generated from beta-binomial distributions. Both symmetric and skewed distributions were used. The sample space consisted of the integers 0(1)4 or 0(1)10. For the global test that is proposed, when testing at the .05 level, simulation estimates of the actual Type I error probability ranged between .043 and .059. For the new multiple comparison procedure, the estimated familywise error rate ranged between .031 and .054 for the sample space 0(1)4. But for 0(1)10, the estimates dropped as low as .016 in some situations. Given the goal of comparing means, Student’s t is well-known to have practical problems when distri¬butions differ. Similar problems are found here among the situations considered. No single method dominates in terms of power, as would be expected, because different methods are sensitive to different features of the distributions being compared. But in general, one of the new methods tends to have relatively good power based on both simulations and experience with data from actual studies. If, however, there is explicit interest in comparing means, rather than comparing the cell probabilities, Welch’s test was found to perform well. The new methods are illustrated using data from the Well-Elderly Study where the goal is to compare groups in terms of depression and the strategies used for dealing with stress.
Vacuum Electronics, International Conference, 2000
IOTs (inductive output tubes) are relatively novel vacuum electron devices that have established ... more IOTs (inductive output tubes) are relatively novel vacuum electron devices that have established their position as reliable and highly efficient UHF amplifiers, predominantly in the television transmitter service. In this application, they reach output power levels equivalent to about 50 kW CW. Scientific applications, like proton accelerators, require UHF amplifiers with considerably higher output power capability. Super power klystrons are
Psychological studies in general, and psy-chobiological studies in particular, routinely use a co... more Psychological studies in general, and psy-chobiological studies in particular, routinely use a collec-tion of classic statistical techniques aimed at comparing groups or studying associations. A fundamental issue is whether violating the basic assumptions underlying these methods, namely normality and homoscedasticity, can result in relatively poor power or miss important features of the data that have practical significance. In the statistics literature, hundreds of papers make it clear that under general conditions the answer is yes and that routinely used strategies for dealing with violations of assumptions can be unsatisfactory. Moreover, a vast ar-ray of new and improved techniques is now available for dealing with violations of assumptions, including more flexible methods for dealing with curvature. The pa-per reviews the major insights regarding standard meth-ods, explains why some seemingly reasonable methods for dealing with violations of assumptions are technically unsoun...
Angular impulse generation is dependent on the position of the total body center of mass (CoM) re... more Angular impulse generation is dependent on the position of the total body center of mass (CoM) relative to the ground reaction force (GRF) vector during contact with the environment. The purpose of this study was to determine how backward angular impulse was regulated during two forward translating tasks. Control of the relative angle between the CoM and the GRF was hypothesized to be mediated by altering trunk-leg coordination. Eight highly skilled athletes performed a series of standing reverse somersaults and reverse timers. Sagittal plane kinematics, GRF, and electromyograms of lower extremity muscles were acquired during the take-off phase of both tasks. The magnitude of the backward angular impulse generated during the push interval of both tasks was mediated by redirecting the GRF relative to the CoM. During the reverse timer, backward angular impulse generated during the early part of the take-off phase was negated by limiting backward trunk rotation and redirecting the GRF ...
When data are nonnormal in form classical procedures for assessing treatment group equality are p... more When data are nonnormal in form classical procedures for assessing treatment group equality are prone to distortions in rates of Type I error and power to detect effects. Replacing the usual means with trimmed means reduces rates of Type I error and increases sensitivity to detect effects. If data are skewed, say to the right, then it has been postulated that asymmetric trimming, to the right, should be better at controlling rates of Type I error and power to detect effects than symmetric trimming from both tails of the data distribution. Keselman, Wilcox, Othman and Fradette (2002) found that Babu, Padmanabhan and Puri's (1999) test for symmetry when combined with a heteroscedastic statistic which compared either symmetrically or asymmetrically determined means provided excellent Type I error control even when data were extremely heterogeneous and very nonnormal in form. In this paper, we present a detailed discussion of the Babu et al. procedure as well as a numerical example ...
Communications in Statistics - Simulation and Computation, 2014
ABSTRACT Simulation results are reported on methods that allow both within group and between grou... more ABSTRACT Simulation results are reported on methods that allow both within group and between group heteroscedasticity when testing the hypothesis that independent groups have identical regression parameters. The methods are based on a combination of extant techniques, but their finite-sample properties have not been studied. Included are results on the impact of removing all leverage points or just bad leverage points. The method used to identify leverage points can be important and can improve control over the Type I error probability. Results are illustrated using data from the Well Elderly II study.
Fifth IEEE International Vacuum Electronics Conference (IEEE Cat. No.04EX786), 2004
Summary form only given. Irrespective of the type RF device, the starting point for RF power prod... more Summary form only given. Irrespective of the type RF device, the starting point for RF power production is generation of a high quality electron beam. The quality of the electron beam is determined by the optical design of the gun and the quality of the cathode. Unfortunately, RF engineers have insufficient control of cathode quality. A vacuum test facility has
The Welch-James and Improved General Approximation tests were examined in between-subjects × with... more The Welch-James and Improved General Approximation tests were examined in between-subjects × within-subjects repeated measures designs for their rates of Type I error when data were nonnormal, nonspherical, and heterogeneous and when group sizes were unequal as well. The tests were computed with either least squares or robust estimators of central tendency and variability and assessed with critical values that
ABSTRACT The paper describes two new methods for comparing two independent, discrete distri¬butio... more ABSTRACT The paper describes two new methods for comparing two independent, discrete distri¬butions, when the sample space is small, using an extension of the Storer–Kim method for comparing independent binomials. These methods are relevant, for example, when compar¬ing groups based on a Likert scale, which was the motivation for the paper. In essence, the goal is to test the hypothesis that the cell probabilities associated with two independent multinomial distributions are equal. Both a global test and a multiple comparison procedure are proposed. The small-sample properties of both methods are compared to four other techniques via simulations: Cliff’s generalization of the Wilcoxon–Mann–Whitney test that effectively deals with heteroscedasticity and tied values, Yuen’s test based on trimmed means, Welch’s test and Student’s t test. For the simulations, data were generated from beta-binomial distributions. Both symmetric and skewed distributions were used. The sample space consisted of the integers 0(1)4 or 0(1)10. For the global test that is proposed, when testing at the .05 level, simulation estimates of the actual Type I error probability ranged between .043 and .059. For the new multiple comparison procedure, the estimated familywise error rate ranged between .031 and .054 for the sample space 0(1)4. But for 0(1)10, the estimates dropped as low as .016 in some situations. Given the goal of comparing means, Student’s t is well-known to have practical problems when distri¬butions differ. Similar problems are found here among the situations considered. No single method dominates in terms of power, as would be expected, because different methods are sensitive to different features of the distributions being compared. But in general, one of the new methods tends to have relatively good power based on both simulations and experience with data from actual studies. If, however, there is explicit interest in comparing means, rather than comparing the cell probabilities, Welch’s test was found to perform well. The new methods are illustrated using data from the Well-Elderly Study where the goal is to compare groups in terms of depression and the strategies used for dealing with stress.
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Papers by Rand Wilcox