Shift Bias Research Articles

Determination of the local contact potential difference of PTCDA on NaCl: a comparison oftechniques

There has been increasing focus on the use of Kelvin probe force microscopy (KPFM) forthe determination of local electronic structure in recent years, especially in systems whereother methods, such as scanning tunnelling microscopy/spectroscopy, may be intractable.We have examined three methods for determining the local apparent contactpotential difference (CPD): frequency modulation KPFM (FM-KPFM), amplitudemodulation KPFM (AM-KPFM), and frequency shift–bias spectroscopy, on a testsystem of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on NaCl, anexample of an organic semiconductor on a bulk insulating substrate. We willdiscuss the influence of the bias modulation on the apparent CPD measurementby FM-KPFM compared to the DC-bias spectroscopy method, and provide acomparison of AM-KPFM, AM–slope detection KPFM and FM-KPFM imagingresolution and accuracy. We will also discuss the distance dependence of the CPD asmeasured by FM-KPFM for both the PTCDA organic deposit and the NaCl substrate.

Measuring Change in a Short-Term Educational Program Using a Retrospective Pretest Design

The Pennsylvania Governor's School for International Studies is an intensive summer program designed to give talented high school students a challenging introduction to the study of international affairs. One focus of the evaluation seeks to understand the effect of the program on the students' perception of their knowledge concerning core issues. Across the long history of the program, a variety of measures were used (and subsequently discarded) to assess changes in knowledge and perception of competence. Four years ago the program instituted a retrospective pre-post design. Results from these years, indicate that these students have consistently overestimated their pre-test understanding of core competencies emphasized in the program and that they seem better able to assess their knowledge gains and their initial inflated sense of knowledge as a result of the program. This article offers an overview of the development, application, use and analysis of a retrospective pre-post instrument to address response shift bias.

Spectral Analysis of Irregularly Sampled Data with Time Series Models

Slotted resampling transforms an irregularly sampled process into an equidistant missing-data problem. Equidistant resampling inevitably causes bias, due to aliasing and the shift of the irregular observation times to an equidistant grid. Taking a slot width smaller than the resampling time can diminish the shift bias. A dedicated estimator for time series models of multiple slotted data sets with missing observations has been developed for the estimation of the power spectral density and of the autocorrelation function. The algorithm estimates time series models and selects the order and type from a number of candidates. It is tested with benchmark data. Spectra can be estimated until frequencies higher than 100 times the mean data rate.

Optimal assignment of multiple utilities in heat exchange networks

Existing numerical geometry-based techniques, developed by [A.I.A. Salama, Numerical techniques for determining heat energy targets in pinch analysis, Computers & Chemical Engineering 29 (2005) 1861–1866; A.I.A. Salama, Determination of the optimal heat energy targets in heat pinch analysis using a geometry-based approach, Computers & Chemical Engineering 30 (2006) 758–764], have been extended to optimally assign multiple utilities in heat exchange network (HEN). These techniques utilize the horizontal shift between the cold composite curve ( CC) and the stationary hot CC to determine the HEN optimal energy targets, grand composite curve ( GCC), and the complement grand composite curve (CGCC). The proposed numerical technique developed in this paper is direct and simultaneously determines the optimal heat-energy targets and optimally assigns multiple utilities as compared with an existing technique based on sequential assignment of multiple utilities. The technique starts by arranging in an ascending order the HEN stream and target temperatures, and the resulting set is labelled T . Furthermore, the temperature sets where multiple utilities are introduced are arranged in an ascending order and are labelled T ic and T ih for the cold and hot sides, respectively. The graphical presentation of the results is facilitated by the insertion at each multiple-utility temperature a perturbed temperature equals the insertion temperature minus a small perturbation. Furthermore, using the heat exchanger network (HEN) minimum temperature-differential approach (Δ T min) and stream heat-capacity flow rates, the presentation is facilitated by using the conventional temperature shift of the HEN CCs. The set of temperature-shifted stream and target temperatures and perturbed temperatures in the overlap range between the CCs is labelled T ol . Using T ol , a simple formula employing enthalpy-flow differences between the hot composite curve CC h and the cold composite curve CC c is used to determine the horizontal shift (bias) B between the CCs. In the overlap range, the Bs are determined at all temperatures in set T ol to generate the bias set B . The maximum value of B’s in set B , B*, is used in an optimization scheme to determine the optimal assignment of multiple utilities, optimal heat- energy targets, grand composite curve ( GCC), and the complement grand composite curve ( CGCC) (Salama, 2009), if needed. It should be pointed out that the optimal heat-energy targets and optimal multiple utilities are needed in heat-pinch analysis. The motivations for the present work is to complement the work of Shenoy [U.V. Shenoy, A. Sinha, S. Bandyopadhyay, Multiple utilities targeting for heat exchanger networks, Trans Institution of Chemical Engineers Part A, 76 (1998) 259–272], by approaching the multiple-utility targeting not sequential but rather in a direct manner. Furthermore, the proposed technique builds on the strengths of the numerical techniques developed by Salama [A.I.A. Salama, Numerical techniques for determining heat energy targets in pinch analysis, Computers & Chemical Engineering 29 (2005)1861–1866; A.I.A. Salama, Determination of the optimal heat energy targets in heat pinch analysis using a geometry-based approach, Computers & Chemical Engineering 30 (2006) 758–764], which are different from the conventional one that starts with the problem table algorithm ( PTA). The proposed technique starts with the determination of the optimally positioned CCs and then proceeds to determine the optimal heat energy targets, heat pinch-point location, grand composite curve ( GCC), complement grand composite curve ( CGCC) [A.I.A. Salama, Numerical construction of HEN composite curves and their attributes, Computers & Chemical Engineering, 33 (2009) 181–190], and optimal assignment of multiple utilities. Moreover, the proposed numerical technique can handle both quasi-linear CCs and CCs exhibiting discontinuities (assuming the critical lower bound on Δ T min , Δ T min c , is known) hence, it is more robust and versatile and avoids the lumping and cascading stages in the PTA. It should be emphasized that the optimal heat loads are determined using the HEN CCs. The associated optimization problems are implemented using Microsoft Excel TM and are solved using the “solver” module embedded in Excel. Published data set has been used to demonstrate the paper results.

Controlling response shift bias: the use of the retrospective pre‐test design in the evaluation of a master's programme

Traditionally the measures used to evaluate the impact of an educational programme on student outcomes and the extent to which students change is a comparison of the student's pre‐test scores with his/her post‐test scores. However, this method of evaluating change may be problematic due to the confounding factor of response shift bias when student self‐reports of change are used. Response shift bias occurs when the student's internal frame of reference of the construct being measured, for example research ability or critical thinking, changes between the pre‐test and the post‐test due to the influence of the educational programme. To control for response shift bias the retrospective pre‐test method was used to evaluate the outcomes achieved from students completing a research module at master's level. The retrospective pre‐test method differs from the traditional pre‐test–post‐test design in that both post‐test and pre‐test perceptions of respondents are collected at the same time. The findings indicated that response shift bias was evident in that the programme had significantly greater impact on outcomes than identified using the traditional pre‐test–post‐test design leading to the conclusion that students may overestimate their ability at the commencement of an educational programme. The retrospective pre‐test design is not a replacement for the traditional pre‐test–post‐test measures but may be a useful adjunct in the evaluation of the impact of educational programmes on student outcomes.

Effect of sequential applications of topical tacrolimus and topical corticosteroids in the treatment of pediatric atopic dermatitis: An open-label pilot study

The efficacy of combination therapy with topical corticosteroids and tacrolimus in the treatment of atopic dermatitis remains to be established. Our aim was to determine whether a regimen of sequential application of topical corticosteroids and topical tacrolimus is effective in the treatment of pediatric atopic dermatitis. A second goal was to assess the impact of this treatment regimen on quality of life (QOL) and the response shift on QOL changes. The study regimen consisted of 3 phases. In the induction phase, patients were treated for a 2-week period with application of 0.03% tacrolimus ointment in the morning and application of a strong- or weak-potency corticosteroid ointment in the evening. In the transitional phase, they were treated for an additional 2 weeks with 0.03% tacrolimus ointment twice daily on weekdays and concurrent application of tacrolimus and a topical corticosteroid ointment on weekend days. In the maintenance phase, the corticosteroid ointment was discontinued and 0.03% tacrolimus ointment was applied twice daily for an additional 2 weeks. Daily application of tacrolimus ointment was then discontinued and replaced by an emollient with application of 0.03% tacrolimus ointment only when necessary for an additional 6 weeks. The Eczema Area and Severity Index score, Investigators' Global Assessment, severity of pruritus and sleep disturbance scores, and QOL evaluation were measured. After 12 weeks, the patients completed a retrospective version of the pretreatment QOL evaluation for analysis of response shift bias. Eczema Area and Severity Index scores decreased by the sixth week, and continued improvement was observed during an additional 6-week period. Both the pruritus and sleep disturbance scores decreased throughout the study. Of patients, 90% showed marked clinical improvement at week 6 and 96% at week 12. On the Children's Dermatology Life Quality Index and the Infant's Dermatology QOL Index survey, mean QOL scores improved after completion of therapy at week 12. The mean difference between the pretest and the retrospective pretest scores indicated the presence of a response shift bias. This was an uncontrolled, open-label study. Conclusions are limited by the small sample size. A fixed sequential regimen of application of tacrolimus ointment with tapering of topical corticosteroids may limit the long-term use and adverse effects of topical corticosteroids, while maintaining clinical control of pediatric atopic dermatitis and improving the QOL. The finding of a response shift bias suggests that parents/guardians underestimate the seriousness of skin disease and its impact on QOL.

Curriculum Evaluation and Revision in a Nascent Field

Although most academic disciplines evolve at a measured pace, the emerging field of homeland security must, for reasons of safety and security, evolve rapidly. The Department of Homeland Security sponsored the establishment of a graduate educational program for key officials holding homeland security roles. Because homeland security is a nascent field, the establishment of a program curriculum was forced to draw from a variety of disciplines. Curriculum evaluation was complicated by the rapid changes occurring in the emerging discipline, producing response shift bias, and interfering with the pre-post assessments. To compensate for the validity threat associated with response shift bias, a retrospective pretest-posttest evaluative methodology was used. Data indicate the program has evolved in a significant and orderly fashion and these data support the use of this innovative evaluation approach in the development of any discipline.

Expression and Suppressive Effects of Interleukin-19 on Vascular Smooth Muscle Cell Pathophysiology and Development of Intimal Hyperplasia

Anti-inflammatory cytokines may play a protective role in the progression of vascular disease. The purpose of this study was to characterize interleukin (IL)-19 expression and function in the development of intimal hyperplasia, and discern a potential mechanism of its direct effects on vascular smooth muscle cells (VSMCs). IL-19 is an immunomodulatory cytokine, the expression of which is reported to be restricted to inflammatory cells. In the present study, we found that IL-19 is not expressed in quiescent VSMCs or normal arteries but is induced in human arteries by injury and in cultured human VSMCs by inflammatory cytokines. Recombinant IL-19 significantly reduced VSMC proliferation (37.1 +/- 4.8 x 10(3) versus 72.2 +/- 6.1 x 10(3) cells/cm(2)) in a dose-dependent manner. IL-19 adenoviral gene transfer significantly reduced proliferation and neointimal formation in balloon angioplasty-injured rat carotid arteries (0.172 +/- 29.9, versus 0.333 +/- 71.9, and 0.309 +/- 56.6 microm(2)). IL-19 induced activation of STAT3 as well as the expression of the suppressor of cytokine signaling 5 (SOCS5) in VSMCs. IL-19 treatment significantly reduced the activation of p44/42 and p38 MAPKs in stimulated VSMCs. Additionally, SOCS5 was found to interact with both p44/42 and p38 MAPKs in IL-19-treated human VSMCs. This is the first description of the expression of both IL-19 and SOCS5 in VSMCs and of the functional interaction between SOCS5 and MAPKs. We propose that through induction of SOCS5 and inhibition of signal transduction, IL-19 expression in VSMCs may represent a novel, protective, autocrine response of VSMCs to inflammatory stimuli.

Overview of Agreement Statistics for Medical Devices

This paper is an overview that summarizes recently developed tools in assessing agreement for methods comparison and instrument/assay validation in medical devices. This paper emphasizes concept, sample sizes, and examples more than analytical formulas. We have considered a unified approach of evaluating agreement among multiple instruments (k), each with multiple replicates (m) for both continuous and categorical data. We start with the basic scenario of two instruments (k = 2), each with only one measurement (m = 1). In this basic scenario for continuous data, we also consider if the target values are considered random (values of a gold standard instrument) or fixed (known values). In the more general case, we will not consider when the target values are fixed. We discuss the simplified sample size calculations. When there is a disagreement between methods, one needs to know if the source of the disagreement was due to a systematic shift (bias) or random error. The coefficients of accuracy and precision will be discussed to characterize these sources. This is important because a systematic shift usually can be easily fixed through calibration, while a random error usually is a more cumbersome variation reduction exercise. For categorical variables, we consider scaled agreement statistics. For continuous variables, we use scaled or unscaled agreement statistics. For variables with proportional error, we can simply apply a log transformation to the data. Finally, three examples are given: one for assay validation, one for a lab proficiency assessment, and one for a lab comparison on categorical assay.

Time series models for spectral analysis of irregular data far beyond the mean data rate

Slotted resampling transforms an irregularly sampled process into an equidistantly sampled signal where data are missing. Equidistant resampling always causes spectral bias, due to aliasing and to shifting of the observation times. The shift bias can be diminished by using a slot width that is smaller than the resampling time step. A special approximate maximum likelihood time series estimator has been developed to estimate the power spectral density and the autocorrelation function of multi-shift slotted nearest-neighbour resampled data sets with missing observations. The algorithm estimates several time series models and selects the best model order and model type from a number of candidates. It is tested with benchmark data. It can estimate spectra up to frequencies more than a thousand times higher than the mean data rate. It can be applied to various irregularly sampled data, including bubbly turbulent flow and very sparse climate or atmospheric data.

Food-specific spatial memory biases in an omnivorous bird

The tendency of nectarivorous birds to perform better on tasks requiring them to avoid previously rewarding locations (to win-shift) than to return to them (win-stay) has been explained as an adaptation to the depleting nature of nectar. This interpretation relies on the previously untested assumption that the win-shift tendency is not associated with food types possessing a different distribution. To test this assumption, we examined the specificity of this bias to different food types in an omnivorous honeyeater, the noisy miner (Manorina melanocephala). As predicted, we found that the win-shift bias was sensitive to foraging context, manifesting only in association with foraging for nectar, not with foraging for invertebrates.

Determination of the optimal heat energy targets in heat pinch analysis using a geometry-based approach

A simple and direct numerical technique is proposed to determine the optimal heat energy targets in heat pinch analysis. The technique is based on a geometrical approach, i.e., utilization of the horizontal shift between the cold composite curve (CC) and the stationary hot CC. The stream and target temperatures of the streams are a subset of an ordered set to form the overall temperature range ▪. If the temperature subinterval in the overlap region of the CCs is equal to the minimum temperature differential Δ T min, simple formulas that utilize the enthalpy flow values can be used to determine the corresponding horizontal shift (bias) B between the CCs . In the overlap range, Bs are determined at all points on one CC and other points on the other CC using Δ T min to form the set ▪. The maximum value of Bs in set ▪, B*, is used to determine the optimal heat energy targets. If the temperature subinterval in the overlap range is not equal to Δ T min, the conventional temperature shift of the CCs is employed first and the resulting stream and target temperatures of the streams are set ▪. In this case the same algebraic formulas are applicable. Heat pinch locations at end points or on a parallel section on the CCs are discussed. It is shown, again, that the same algebraic formulas are applicable. The proposed technique is different from the conventional one since it starts with the determination of the optimally positioned CCs and then proceeds to determine the optimal heat energy targets, heat pinch point location, and grand composite curve (GCC). In the conventional heat pinch analysis, the problem table algorithm (PTA) is employed first. Furthermore, the present technique is conceptually different from the PTA and the simple problem table algorithm (SPTA) since it is developed based on a geometrical approach not energy cascade over the overlap temperature subintervals. While the PTA and SPTA are only applicable using temperature-shifted data the proposed geometry-based technique is applicable to both shifted- and unshifted-temperature data sets. Moreover, the proposed numerical technique can handle both quasilinear CCs and CCs exhibiting discontinuities (assuming the critical lower bound on Δ T min, Δ T min c , is known) hence, it is more robust and versatile and avoids the lumping and cascading stages in the PTA.

Mapping Contact Potential Differences with Noncontact Atomic Force Microscope Using Resonance Frequency Shift versus Sample Bias Voltage Curves

We have measured cantilever resonance frequency versus sample bias voltage and generated frequency vs bias ( f–V) curves using an ultrahigh-vacuum noncontact atomic force microscope (UHV NC-AFM). Using the f–V data, we calculated the contact potential difference (CPD) between the tip and the sample. These CPD measurements were compared with those that were directly observed with a scanning Kelvin probe force microscope (SKPM) on the same atomically resolved area of the sample using a UHV-AFM. The CPD values obtained by both methods were similar, however, it was difficult to obtain CPD values that agreed precisely on the atomic scale.

An Empirical Evaluation Of The Retrospective Pretest: Are There Advantages To Looking Back?

This article builds on research regarding response shift effects and retrospective self-report ratings. Results suggest moderate evidence of a response shift bias in the conventional pretest-posttest treatment design in the treatment group. The use of explicitly worded anchors on response scales, as well as the measurement of knowledge ratings (a cognitive construct) in an evaluation methodology setting, helped to mitigate the magnitude of a response shift bias. The retrospective pretest-posttest design provides a measure of change that is more in accord with the objective measure of change than is the conventional pretest-posttest treatment design with the objective measure of change, for the setting and experimental conditions used in the present study.

Improving the Evaluation of Leadership Programs: Control Response Shift

The Cooperative Extension Service has been a key partner in the design, implementation and evaluation of leadership development programs. To evaluate the effectiveness of their training and the effects of response shift bias on outcomes using a self-report measure, one hundred forty-seven County Extension Agents participated in this leadership study. Participants were randomly assigned to one of two treatment groups or to a control group. Two different evaluation designs (pre-posttest and then-post) were used. The then-post design asks participants to first report their behavior or understanding as a result of the training (post) and then to retrospectively report this behavior before the training. The then-post evaluation design provided more significant change data than did the traditional pre-posttest design indicating a response shift occurred. Such differences in evaluation findings suggest that the educational benefit of such trainings may be underestimated when using the traditional pre-post evaluation design.

Actual versus self-reported scholastic achievement of litigating postconcussion and severe closed head injury claimants.

Psychologists typically rely on patients' self-report of premorbid status in litigated settings. The authors examined the fidelity between self-reported and actual scholastic performance in litigating head injury claimants. The data indicated late postconcussion syndrome (LPCS) and severe closed head injury litigants retrospectively inflated scholastic performance to a greater degree than nonlitigating control groups. The LPCS group showed the highest magnitude of grade inflation, but discrepancy scores did not significantly correlate with a battery of malingering measures or with objective cerebral dysfunction. These findings support previous studies, which showed self-report is not a reliable basis for estimation of preinjury cognitive status. Retrospective inflation may represent a response shift bias shaped by an adversarial context rather than a form of malingering.

Quality of life in children with otitis media: validity of a survey

Introduction. Validity research into the OM-6 for a Dutch population, quality of life after grommets1 and the influence of ‘response shift bias’ was undertaken. Methods. Parents of 77 children with otitis media (OME) (age 12–36 months) completed the OM-6 (six items, seven-point scale). Quality of life domains concern physical suffering, hearing loss, speech impairment, emotional distress, activity limitations and caregiver concerns. The ‘global quality of life’ rating is performed on a 10-point visual analogue scale. The OM-6 is completed after the first visit to the ear, nose and throat (ENT) surgeon (pre-test 1) and around the time of surgery (pre-test 2). The post-test and the retrospective pre-test are scheduled 6 weeks after the intervention. Results. ‘Global quality of life’ and OM-6 ratings show a good correlation (R = −0.77, P < 0.01). Internal consistency of the OM-6 is satisfying (α = 0.79), responsiveness to clinical change is large (standardized response mean >0.8). Response shift bias is expressed by a difference between pre-test 1 and the retrospective pre-test (T = −3.3, P < 0.01). Before surgery, parents underestimate the seriousness of hearing loss (Z = −3.3, P < 0.05) and overestimate quality of life in general (Z = −3.6, P < 0.05). Conclusion. The OM-6 is valid for a Dutch population. Reported quality of life improves as a consequence of the intervention. The presence of response shift could be explained through adaptation to symptoms before surgery and changes in symptoms as a result of surgery, as well as an increase in knowledge of the consequences related to OME and hearing loss.

Nonlinear Behavior under Regional Neutron Flux Oscillations in BWR Cores

A three-dimensional time-domain core analysis code was applied to numerical simulations for an actual regional neutron flux oscillation observed in a commercial BWR core, in order to investigate potential nonlinear behavior in its coupled neutronic and thermohydraulic system. The present study shows existence of the nonlinear reactivity interaction between the fundamental and first azimuthal spatial harmonics modes of neutron flux distribution under the regional event. The spectrum analysis of the simulated data provides a unique result, that is, temporal harmonics peaks are excited at the even- and odd-order multiples of the characteristic resonance frequency in the fundamental and first spatial harmonics responses, respectively. The numerical simulation also shows that the strong nonlinearity of the coupled neutronic and thermohydraulic dynamics locally appears where the power unstably oscillates with large amplitudes, inducing the power shift and reactivity bias which are shown in the core-wide situation under the global oscillations. This contributes to suppression of the divergence of the local power oscillation, and also to development of the saturated self-limited cycles under the regional oscillations.

Response Shift Bias: A Problem in Evaluating Nutrition Training Using Self-Report Measures

The Cooperative Extension Service has been a key partner in the design, implementation, and evaluation of school nutrition training. To evaluate the effectiveness of their training and the effects of response shift bias on outcomes using a self-report measure, 162 foodservice staff from eight rural schools participated in this food-handling behavior study. Nutrition staff were assigned to one of two treatment groups or to the control group. Two different evaluation designs (pre-test/post-test and then/post) were used. The then/post design asks participants to first report their behavior or understanding as a result of the training (post) and then to retrospectively report this behavior before the training. The then/post evaluation design provided more significant change data than did the traditional pretest/post-test design, indicating that a response shift occurred. Such differences in evaluation findings suggest that the educational benefit of such trainings may be underestimated when using the traditional pre/post evaluation design.

Measuring Program Outcomes: Using Retrospective Pretest Methodology

This study used longitudinal data from 307 mothers with firstborn infants participating in a home-visitation, child-abuse prevention program. A self-report measure of specific constructs the program hoped to affect showed that the retrospective pretest methodology produced a more legitimate assessment of program outcomes than did the traditional pretest-posttest methodology. Results showed that when response shift bias was present, traditional pretest-posttest comparisons resulted in an underestimation of program effects that could easily be avoided by the retrospective pretest methodology. With demands for documenting program outcomes increasing, retrospective pretest designs are shown to be a simple, convenient, and expeditious method for assessing program effects in responsive interventions. The limits of retrospective pretests, and methods for strengthening their use, are discussed.