Stratification bias in low signal microarray studies

BACKGROUND: When analysing microarray and other small sample size biological datasets, care is needed to avoid various biases. We analyse a form of bias, stratification bias, that can substantially affect analyses using sample-reuse validation techniques and lead to inaccurate results. This bias is due to imperfect stratification of samples in the training and test sets and the dependency between these stratification errors, i.e. the variations in class proportions in the training and test sets are negatively correlated. RESULTS: We show that when estimating the performance of classifiers on low signal datasets (i.e. those which are difficult to classify), which are typical of many prognostic microarray studies, commonly used performance measures can suffer from a substantial negative bias. For error rate this bias is only severe in quite restricted situations, but can be much larger and more frequent when using ranking measures such as the receiver operating characteristic (ROC) curve and area under the ROC (AUC). Substantial biases are shown in simulations and on the van 't Veer breast cancer dataset. The classification error rate can have large negative biases for balanced datasets, whereas the AUC shows substantial pessimistic biases even for imbalanced datasets. In simulation studies using 10-fold cross-validation, AUC values of less than 0.3 can be observed on random datasets rather than the expected 0.5. Further experiments on the van 't Veer breast cancer dataset show these biases exist in practice. CONCLUSION: Stratification bias can substantially affect several performance measures. In computing the AUC, the strategy of pooling the test samples from the various folds of cross-validation can lead to large biases; computing it as the average of per-fold estimates avoids this bias and is thus the recommended approach. As a more general solution applicable to other performance measures, we show that stratified repeated holdout and a modified version of k-fold cross-validation, balanced, stratified cross-validation and balanced leave-one-out cross-validation, avoids the bias. Therefore for model selection and evaluation of microarray and other small biological datasets, these methods should be used and unstratified versions avoided. In particular, the commonly used (unbalanced) leave-one-out cross-validation should not be used to estimate AUC for small datasets

After the Bubble: The Survival and Ownership of Internet Marketplaces for Farmers and Agribusiness

This paper presents a theory of how industry structure and beliefs about Internet marketplace use have driven choice and ownership of marketplaces. The theory's predictions suggest that surviving Internet marketplaces will be those with strong historical linkages in an industry and those owned by or affiliated with major commodity buyers. Comparisons of these predictions with actual outcomes provide validation of the theory. Where predictions differ from results, observations are made as to the nature of the deviations.agricultural markets, electronic commerce, Internet markets, network externalities, technology adoption, Agribusiness,

Brand Equity Perceptual Mapping: Competitive Landscapes and Consumer Segments in Brand Equity Space

This study advanced a technique to map brand metrics and theoretically derived diagnostics that depict the relative positions of competitive brand sets and audience segments in a perceptual consumer-based brand equity space. Survey research collected brand equity ratings for two sets of competitive brands (Nike, Converse, Reebok and Toyota, Nissan, Pontiac), used to construct a pair of twodimensional maps that illustrate the brands’ position on brand equity dimensions relative to competitors and demographic-based segments. Paired brand equity indicators resulted in eight map quadrant areas that characterize a brand positioned in that space. The mapping techniques facilitate the strategic application of multidimensional brand equity constructs and their use as brand valuation tools

Positivity and Positive Reinforcement in Organizational Culture at Nazarene Higher Education Institutions

Given the importance of employee motivation, satisfaction, productivity, and retention, as well as the support for positivity in the review of the literature, this study examined the effects of positivity and positive reinforcement in organizational culture, through the lens of admissions professionals, at the eight Nazarene Higher Education Institutions (NHEI) within the United States. The study also examined the effects of the perceived positivity of leaders in organizational culture, in the same context. The findings revealed some signs of positivity among NHEI admissions professionals, but no evidence was revealed regarding the consistent use of positive reinforcement in these settings. The perceived positivity of administrators was determined to be important to these NHEI admissions professionals

The Influence of Brand Equity on Consumer Response toward Environmental Product Advertisements

This study reports an examination of the relationship between a three-factor brand equity measure (brand awareness, brand quality, and brand loyalty) and consumer response toward environmental product advertisements for four brands (i.e., Whole Foods, Green Works, Prius, and Volt). An online, digital survey allowed the presentation of television commercials and accompanying response measures including green brand trust, perceived ad claim believability, and attitude-toward-the-ad. Results illustrate significant relationships between brand equity with the green trust and claim believability measures, but not with attitude toward the advertisements. Analysis also illustrated the interrelationships between the response variables and showed of the brand equity dimensions, perceived brand quality, and especially brand loyalty, had significant relationships with the green brand trust and ad claim believability measures. In addition, brand image was a significant factor only for the automobile brands, indicating a possible category effect, where this brand equity factor is relevant. Results suggest that preexistent brand dispositions influence perceived environmental ad believability and trust, critical factors, which have a significant influence on message effectiveness

Design, implementation and testing of a digital baseband receiver for spread spectrum telesensing

Telesensing involves receiving data wirelessly from a remote sensor Generally, the sensor node is fixed and configured to transmit only or perform very basic reception Because of their low power consumption, telesensors can be powered by a battery for long periods of time without a measurement or transmission interruption This allows several nodes to be placed at strategic locations and creates a need to have all the individual data collected and processed at a centralized location Frequency Division Multiple Access (FDMA) provides robust data transmission from multiple telesensors to the same receiver at the cost of added bandwidth. This thesis focuses on the digital recovery of spread spectrum data in an FDMA system A general digital spread spectrum receiver architecture is given(without transceiving capability) and each component is designed,implemented and tested m the receiver as a whole A sliding correlator with a threshold is used to synchronize the pseudonoise (PN) code used to encode the data with the incoming data System clocks are also recovered from the incoming data and distributed to the downstream modules The design is implemented in an FPGA and tested with favorable packet error rate results m an FDMA system The components of the digital receiver processor could be used in conjunction with a Costas Loop demodulator to provide CDMA for multiple sensors and its functionality and robustness are confirmed in this thesis This would fit into a complete CDMA, allowing the demodulator to discriminate between various sensor

A New Drag Measurement System for Wind Tunnel Testing of the Racing Bicycle and Rider to Determine a Low Drag Configuration

This study investigated the application of splitter plate effects to reduce the aerodynamic drag of the racing bicycle and rider system. A sensitive, low-force, beam-type, single-component balance was developed to provide drag measurements accurate to within 0.053 N (0.012 lbf). The performance of the new system was verified by comparing the measured drag on a three-dimensioaal, right-circular cylinder model, 0.127 m (5.0 in) in diameter and 0.610 m (24 in) long, with the results from a commercial balance and a other similar data. The bicycle and rider model consisted of a full-scale mannequin comprising only the hips, legs and feet, mounted on a regulation 0.48 m (19 in) size bicycle. Rotation of the wheels and a stationary ground plane were also simulated. Two frame configurations in conjunction with a disk type wheel were tested to determined the lowest drag configuration for narrow and wide spacing of the rider\u27s legs. The results show that for the standard tube construction frame, the conventional wisdom to streamline as much as possible prevails. When an aerodynamic frame was tested, the overall drag was reduced. Although the standard spacing still provided the lowest drag configuration, any further streamlining showed an increase in drag

Brand Equity Perceptual Mapping: Competitive Landscapes and Consumer Segments in Brand Equity Space

This study put forward a theoretically based set of brand equity perceptual maps that depict competitive brand sets and consumer segments in four-dimension brand equity space. Survey research collected brand equity ratings for two sets of competitive brands (Nike, Converse, Reebok and Toyota, Nissan, Pontiac), used to construct a pair of two-dimensional maps that illustrate the brands’ position on brand equity dimensions relative to competitors and demographic-based segments. Paired brand equity indicators resulted in eight map quadrant areas that characterize a brand positioned in that space. The mapping techniques facilitate the strategic application of multidimensional brand equity constructs and their use as brand valuation tools