Search results for " Least squares"
showing 10 items of 223 documents
Prediction Accuracy of a Novel Dynamic Structure-Function Model for Glaucoma Progression
2014
Purpose To assess the prediction accuracy of a novel dynamic structure-function (DSF) model to monitor glaucoma progression. Methods Longitudinal data of paired rim area (RA) and mean sensitivity (MS) from 220 eyes with ocular hypertension or primary open-angle glaucoma enrolled in the Diagnostic Innovations in Glaucoma Study or the African Descent and Glaucoma Evaluation Study were included. Rim area and MS were expressed as percent of mean normal based on an independent dataset of 91 healthy eyes. The DSF model uses centroids as estimates of the current state of the disease and velocity vectors as estimates of direction and rate of change over time. The first three visits were used to pre…
Weighted Least-Squares Likelihood Ratio Test for Branch Testing in Phylogenies Reconstructed from Distance Measures
2005
A variety of analytical methods is available for branch testing in distance-based phylogenies. However, these methods are rarely used, possibly because the estimation of some of their statistics, especially the covariances, is not always feasible. We show that these difficulties can be overcome if some simplifying assumptions are made, namely distance independence. The weighted least-squares likelihood ratio test (WLS-LRT) we propose is easy to perform, using only the distances and some of their associated variances. If no variances are known, the use of the Felsenstein F-test, also based on weighted least squares, is discussed. Using simulated data and a data set of 43 mammalian mitochondr…
Influence of Advertising on Brand Personality in The Airline Sector: The Case of Spain
2013
This article outlines the findings of a study employing a partial least squares (PLS) structural equation methodology to explore the relationship among advertising and brand personality (BP) dimension of a validated Aaker's model (1997) in the airline business. BP refers to the emotional side of brand image. It is created by all experiences of consumers with a brand. The model was validated using confirmatory factor analysis and the effect of advertising on BP has been tested using PLS. The findings suggest that advertising influences the formation of BP only in the sophistication dimension. These results invite managers in the airline companies sector to develop communication strategies to…
Dimensions of cosmopolitanism and their influence on political consumption: an analysis focused on Spanish consumers
2013
The purpose of this study was to confirm the hypothesis that political consumption ‐ a form of consumerism whose importance has increased during the past few years ‐ can be considered a form of critical action, and that cosmopolitanism contributes to its development. The main objective was, first, to analyse an unexplored dimension of political consumption and, second, to obtain a measurement proposal for what some authors have called ordinary cosmopolitanism. The study, based on a survey, was divided into three sections. The first section offers a theoretical introduction to the study proposal. The second describes the hypothesis and the data analysis strategy, and proposes an operationali…
Conversion rate determinants in e-commerce websites. What about moderation effects?
2018
Online retailers invest significant resource to improve conversion rates, defined as the proportion of website visitors that make a purchase. Using 1,184 observations from six e-commerce websites, this paper aims to analyse conversion rate determinants, also considering moderation effects of seasonality and webpage speed of load. Results show that free shipping and discounts policy have a positive effect on the conversion rate, moderated by seasonality and load speed. These finding could be useful guidelines for e-commerce managers in order to allocate their limited resources to the most relevant factor to increase online sales.
Marketing or methodology? : Exposing the fallacies of PLS with simple demonstrations
2023
Purpose Over the past 20 years, partial least squares (PLS) has become a popular method in marketing research. At the same time, several methodological studies have demonstrated problems with the technique but have had little impact on its use in marketing research practice. This study aims to present some of these criticisms in a reader-friendly way for non-methodologists. Design/methodology/approach Key critiques of PLS are summarized and demonstrated using existing data sets in easily replicated ways. Recommendations are made for assessing whether PLS is a useful method for a given research problem. Findings PLS is fundamentally just a way of constructing scale scores for regression. PL…
Rejoinder: fractures in the edifice of PLS
2023
Purpose This study aims to provide a response to the commentary by Yuan on the paper “Marketing or Methodology” in this issue of EJM. Design/methodology/approach Conceptual argument and statistical discussion. Findings The authors find that some of Yuan’s arguments are incorrect, or unclear. Further, rather than contradicting the authors’ conclusions, the material provided by Yuan in his commentary actually provides additional reasons to avoid partial least squares (PLS) in marketing research. As such, Yuan’s commentary is best understood as additional evidence speaking against the use of PLS in real-world research. Research limitations/implications This rejoinder, coupled with Yuan’s comm…
Mass appraisal of residential real estate using multilevel modelling
2016
Mass appraisal, or the automatic valuation of a large number of real estate assets, has attracted the attention of many researchers, who have mainly approached this issue employing traditional econometric models such as Ordinary Least Squares (OLS). However, this method does not consider the hierarchical structure of the data and therefore assumes the unrealistic hypothesis of the independence of the individuals in the sample. This paper proposes the use of the Hierarchical Linear Model (HLM) to overcome this limitation. The HLM also gives valuable information on the percentage of the variance error caused by each level in the hierarchical model. In this study HLM was applied to a large dat…
Preliminary results on direct quantitative determination of cocaine in impregnated materials by infrared spectroscopy
2018
Abstract Partial least squares models were built for the direct determination of cocaine in seized impregnated smuggled materials. Measurements are based on the attenuated total reflectance middle infrared spectra (ATR-MIR) and diffuse reflectance spectra in the near range (DR-NIR) obtained directly from the surface of the impregnated materials. The aforementioned procedures offer fast, cheap and environmentally friendly green alternatives to the reference method based on the extraction of the drug and its quantification by gas chromatography. Additionally it has been verified that results found are statistically comparable with those obtained by the reference method with root mean square e…
Variable selection for the determination of total polar materials in fried oils by near infrared spectroscopy
2018
Total polar materials (TPM) content is considered as the best indicator and the most common parameter to check the quality of deep-frying oils. The development of simpler and quicker analytical techniques than the available methods to monitor oil quality in restaurants and fried food outlets is an important topic related to the human health. This paper reports a comparison of the variable selection of near infrared (NIR) spectra by multiple linear regression (MLR-NIR) with partial least squares (PLS-NIR) models for the quantification of TPM in fried vegetable oils. The use of PLS-NIR offers an alternative in laboratory bench equipment for the determination of TPM in oils employed for fryin…