Statistical models for market segmentation

It is an essential element of market research that customer preferences are considered and the heterogeneity of these preferences is recognized. By segmenting the market into homogeneous clusters the preferences of customers is addressed. Latent class methodology for conjoint analysis, proposed by Green (2000), is one of the several conjoint segmentation procedures that overcome the limitations of aggregate analysis and priori segmentation. This approach proposes the proportional odds model as a proper statistical model for ordinal categorical data in which the item attributes are included in the linear predictor. The likelihood is maximized through the EM algorithm. This paper considers two extensions of this methodology that incorporate individual characteristics into the models.peer-reviewe

A Novel fMRI Paradigm Suggests that Pedaling-related Brain Activation is Altered after Stroke

The purpose of this study was to examine the feasibility of using functional magnetic resonance imaging (fMRI) to measure pedaling-related brain activation in individuals with stroke and age-matched controls. We also sought to identify stroke-related changes in brain activation associated with pedaling. Fourteen stroke and 12 control subjects were asked to pedal a custom, MRI-compatible device during fMRI. Subjects also performed lower limb tapping to localize brain regions involved in lower limb movement. All stroke and control subjects were able to pedal while positioned for fMRI. Two control subjects were withdrawn due to claustrophobia, and one control data set was excluded from analysis due to an incidental finding. In the stroke group, one subject was unable to enter the gantry due to excess adiposity, and one stroke data set was excluded from analysis due to excessive head motion. Consequently, 81% of subjects (12/14 stroke, 9/12 control) completed all procedures and provided valid pedaling-related fMRI data. In these subjects, head motion was ≤3 mm. In both groups, brain activation localized to the medial aspect of M1, S1, and Brodmann’s area 6 (BA6) and to the cerebellum (vermis, lobules IV, V, VIII). The location of brain activation was consistent with leg areas. Pedaling-related brain activation was apparent on both sides of the brain, with values for laterality index (LI) of –0.06 (0.20) in the stroke cortex, 0.05 (±0.06) in the control cortex, 0.29 (0.33) in the stroke cerebellum, and 0.04 (0.15) in the control cerebellum. In the stroke group, activation in the cerebellum – but not cortex – was significantly lateralized toward the damaged side of the brain (p = 0.01). The volume of pedaling-related brain activation was smaller in stroke as compared to control subjects. Differences reached statistical significance when all active regions were examined together [p = 0.03; 27,694 (9,608) μL stroke; 37,819 (9,169) μL control]. When individual regions were examined separately, reduced brain activation volume reached statistical significance in BA6 [p = 0.04; 4,350 (2,347) μL stroke; 6,938 (3,134) μL control] and cerebellum [p = 0.001; 4,591 (1,757) μL stroke; 8,381 (2,835) μL control]. Regardless of whether activated regions were examined together or separately, there were no significant between-group differences in brain activation intensity [p = 0.17; 1.30 (0.25)% stroke; 1.16 (0.20)% control]. Reduced volume in the stroke group was not observed during lower limb tapping and could not be fully attributed to differences in head motion or movement rate. There was a tendency for pedaling-related brain activation volume to increase with increasing work performed by the paretic limb during pedaling (p = 0.08, r = 0.525). Hence, the results of this study provide two original and important contributions. First, we demonstrated that pedaling can be used with fMRI to examine brain activation associated with lower limb movement in people with stroke. Unlike previous lower limb movements examined with fMRI, pedaling involves continuous, reciprocal, multijoint movement of both limbs. In this respect, pedaling has many characteristics of functional lower limb movements, such as walking. Thus, the importance of our contribution lies in the establishment of a novel paradigm that can be used to understand how the brain adapts to stroke to produce functional lower limb movements. Second, preliminary observations suggest that brain activation volume is reduced during pedaling post-stroke. Reduced brain activation volume may be due to anatomic, physiology, and/or behavioral differences between groups, but methodological issues cannot be excluded. Importantly, brain action volume post-stroke was both task-dependent and mutable, which suggests that it could be modified through rehabilitation. Future work will explore these possibilities

Ethnicity and the Writing of Medieval Scottish history

Historians have long tended to define medieval Scottish society in terms of interactions between ethnic groups. This approach was developed over the course of the long nineteenth century, a formative period for the study of medieval Scotland. At that time, many scholars based their analysis upon scientific principles, long since debunked, which held that medieval 'peoples' could only be understood in terms of 'full ethnic packages'. This approach was combined with a positivist historical narrative that defined Germanic Anglo-Saxons and Normans as the harbingers of advances of Civilisation. While the prejudices of that era have largely faded away, the modern discipline still relies all too often on a dualistic ethnic framework. This is particularly evident in a structure of periodisation that draws a clear line between the 'Celtic' eleventh century and the 'Norman' twelfth. Furthermore, dualistic oppositions based on ethnicity continue, particularly in discussions of the law, kingship, lordship and religion

Epigenetic alterations at synaptic plasticity genes in a genetically heterogeneous rat model of neuropsychiatric disorders

Sensorimotor gating impairments are observed across a range of neuropsychiatric conditions. The prepulse inhibition of the acoustic startle response (PPI) is a validated measure of sensorimotor gating. Genetic and pharmacological manipulations in rodents have shown PPI is regulated by specific brain monoaminergic systems. Using genetically heterogeneous NIH-HS rats, we stratified individuals by %PPI. In low PPI animals, we observed elevated mRNA levels of certain neurotransmitter receptors, including metabotropic glutamate receptor Grm2, dopamine receptors Drd1 and Drd2, serotonin receptors Htr1a and Htr2a, and scaffolding protein Homer1, in the frontal cortex (FC) and striatum (STR). We found Drd2 mRNA levels were significantly increased in the low PPI group in STR. Multinomial regression analysis indicated Grm2 in FC and Grm2 and Drd2 in STR predicted PPI group. Additional studies showed a linear relationship between PPI and Grm2 in FC and Drd2 in STR. To explore possible epigenetic regulation of altered gene transcription, we adapted chromatin immunoprecipitation (ChIP) for novel application in frozen brain tissue. We evaluated abundance of acetylated histone H3 (H3ac) and trimethylation of lysine residue 27 of histone H3 (H3K27me3) at regions upstream of gene transcription start sites. No differences in levels of H3ac or H3K27me3 were observed. Studies assessing abundance of other histone modifications are warranted. These efforts may offer insight on how epigenetic modification leads to altered transcription of synaptic plasticity genes regulating sensorimotor gating observed in neuropsychiatric conditions

Determining Ratios of WIMP-Nucleon Cross Sections from Direct Dark Matter Detection Data

Weakly Interacting Massive Particles (WIMPs) are one of the leading candidates for Dark Matter. So far the usual procedure for constraining the WIMP-nucleon cross sections in direct Dark Matter detection experiments have been to fit the predicted event rate based on some model(s) of the Galactic halo and of WIMPs to experimental data. One has to assume whether the spin-independent (SI) or the spin-dependent (SD) WIMP-nucleus interaction dominates, and results of such data analyses are also expressed as functions of the as yet unknown WIMP mass. In this article, I introduce methods for extracting information on the WIMP-nucleon cross sections by considering a general combination of the SI and SD interactions. Neither prior knowledge about the local density and the velocity distribution of halo WIMPs nor about their mass is needed. Assuming that an exponential-like shape of the recoil spectrum is confirmed from experimental data, the required information are only the measured recoil energies (in low energy ranges) and the number of events in the first energy bin from two or more experiments.Comment: 33 pages, 20 eps figures; v2: typos fixed, references added and updated, revised version for publicatio