Mixture model analysis of complex samples

This paper investigates asymmetric effects of monetary policy over the business cycle. A two-state Markov Switching Model is employed to model both recessions and expansions. For the United States and Germany, strong evidence is found that monetary policy is more effective in a recession than during a boom. Also some evidence is found for asymmetry in the United Kingdom and Belgium. In the Netherlands, monetary policy is not very effective in either regime.

Essays in international market segmentation

The primary objective of this thesis is to develop and validate new methodologies to improve the effectiveness of international segmentation strategies. The current status of international market segmentation research is reviewed in an introductory chapter, which provided a number of methodological and substantive issues that need further attention. These issues are critically assessed and methodologies are developed as potential solutions.In chapter 1, previous research in international segmentation is classified according to three dimensions depicted in Figure 1. In the figure, the first dimension relates to the segmentation basis, the second to segmentation objects, and the third to segmentation methodology. All three dimensions affect the effectiveness of international segmentation strategies. Two key research directions for improving the effectiveness of international segmentation were formulated along these dimensions.The first direction concerns the integration of targeted product and communication strategies by linking product-specific bases with general consumer-level bases. A new methodology is developed to identify cross-national market segments using means-end chain theory. Based on theory founded in consumer behavior, the means-end chain links values (a general consumer-level basis) with benefits and attributes (product-specific bases).Figure 1Three dimensions of international segmentationSuch an approach has the potential to combine product development and communication strategies at the international segment level and may serve as a guiding principle for international marketers to tailor products and advertising messages to the desires of global consumer segments. Chapter 4 provides a model-based methodology for identifying such segments. An international segmentation model was developed that estimates relations between product attributes, benefits of product use, and consumer values at the international segment level, and at the same time identifies those segments. The model builds upon methodological issues that were addressed in chapters 2 and 3 and rests on mixture methodology that, due to its capability of deriving segments based on models of consumer behavior, is particularly effective. In particular, it accounts for the international sampling design and the heterogeneity of response tendencies across countries and consumers.The segmentation model was applied to identify segments in the European yogurt market, using a large sample of European consumers. Four segments were identified, of which one was truly pan-European and the other segments were cross-national. The segments were found to represent distinctive means-end structures and the pattern of links between attributes, benefits, and values gave rise to strategic implications with respect to product development and communication. The segments were found to be related to socio-demographics, consumption patterns, media consumption, and personality data, which contributes to the identifiability and accessibility of the segments. The results suggest that the proposed model-based international segmentation methodology, combining product- and consumer-level bases, has the potential to identify segments of consumers in different countries that are actionable towards product development and advertising strategy.In chapter 5, a different direction is proposed that seeks to improve the effectiveness of international target market selection of expanding companies, by improving the geographic configuration of segments. Whereas consumer segments are more responsive, their typical geographic configuration does not make them accessible with cost efficient logistic operations. Especially if physical distribution represents a major component of total production and marketing costs, it is important that a geographic segment defines one particular area as opposed to dispersed segments that may arise in previous segmentation approaches. A flexible model-based segmentation approach is developed that identifies contiguous geographic segments based on consumer-level data. The model is based on multi-attribute theory of preference formation and accommodates a broad set of strategic restrictions on the segments. Moreover, the model accounts for heterogeneity that is likely to exist within geographic segments.The methodology is illustrated in the international retailing domain, where geographic expansion is an important strategy to attain growth. Based on the importance that consumers attach to different attributes of store image, five geographic segments were identified across regions in seven countries of the European Union. The segments were distinctive in terms of their patterns of image attribute importances, which provides opportunities for expanding retailers to delineate geographic areas to enter and to develop an appropriate image in such areas. The results also demonstrated the accessibility of the segments through advertising media and logistics. In addition, no significant differences were found between the original model and a nested model that does not take the contiguity into account. This means that the actionability of restricting segments to be contiguous does not substantially harm the responsiveness of these segments.Given the often limited rigor of statistical and measurement techniques applied in the area of international segmentation, special attention has been given to methodological issues. Several issues were addressed that may negatively affect international segmentation research findings and methods were developed to deal with these issues.The first issue concerns the segmentation method . International segmentation research demonstrates an excessive reliance on heuristic segmentation techniques, such as cluster analysis. These techniques provide limited flexibility for international segmentation and may not be very effective in recovering response-based segments. The international segmentation methodologies developed in this thesis are model based and rely on insights from state of the art statistical techniques such as mixture and hierarchical Bayes models. Three international segmentation models are described in chapters 2, 4, and 5, and are successfully applied to empirical data. Chapter 5 provided a Bayesian formulation of a new international segmentation model that accommodates within-segment heterogeneity and complex restrictions on the configuration of segments. In chapter 4 it is empirically shown that a new mixture model approach outperforms standard clustering approaches that are traditionally employed in international segmentation.A second methodological issue is related to the estimation of international segmentation models. The importance of international sampling designs had not been acknowledged in the literature on international segmentation and mixture modeling. Previous international segmentation studies did not account for the implicit stratified sampling designs encountered in cross-national data collection. In this thesis the effects of international sampling designs on maximum likelihood estimation of segmentation models are investigated and a framework for accommodating those effects is proposed. A pseudo maximum likelihood procedure is introduced that accommodates complex sample designs for maximum likelihood estimation of finite mixture models. In addition, modified or pseudo-information criteria are suggested for correct estimation of the number of international segments.The effects of not accounting for the sampling design were empirically assessed in an international value segmentation study. The pseudo-maximum likelihood approach was compared to standard maximum likelihood estimation that does not account for the sampling design. The results show that the estimates of segment sizes and segment-level parameters may be severely biased when not accounting for the design in standard maximum likelihood estimation. In addition, the empirical application demonstrated that the use of standard information criteria leads to incorrect inferences about the number of segments. This means that standard estimation methods in international segmentation research may lead to incorrect conclusions and erroneous managerial action.The international segmentation methodology in chapter 4 was based on MEC theory. The traditional measurement technique for means-end chains (laddering) is not suitable for international segmentation. A necessary condition for the validity of international segments is that the basis for segmentation is measured in a valid and reliable way. Measurement instruments should allow collecting large and representative samples and standardization across countries. In this thesis a MEC measurement technique is developed that meets those criteria. The technique is denoted as the association pattern technique (APT), and its validity is further assessed. Two key issues were investigated that may hamper the validity of APT. First, APT implicitly assumes that attribute-benefit and benefit-value links are independent because it measures these links in two separate tasks. The second issue is the convergent validity of APT as compared to the more traditional laddering interview. Consistent support for independence of attribute-benefit and benefit-value links was found across four product categories. Statistical tests of convergent validity of APT and laddering demonstrated that the basic structure revealed by both methods is similar. This suggests that APT is valid for measuring means-end chains and can be used for identifying international consumer segments. The APT method is successfully applied in an international segmentation study in 11 countries.The final methodological issue addressed in this thesis is related to response tendencies , which may hamper the identification of cross-national segments. The APT method may be prone to a respondent's propensity to choose any link. Therefore, the international segmentation model in chapter 4 accounted for differences in those tendencies that may exist between respondents. Based on item response theory, a response threshold approach was developed that allows testing those differences between countries, but also within countries. The results demonstrated that the differences in response tendencies were significant between countries, but also within countries. This means that it is important to account for response tendencies in international segmentation but in domestic segmentation as well.</p

A Monte Carlo study into time aggregation in continuous and discrete-time hazard models.

This paper introduces a general, formal treatment of dynamic constraints, i.e., constraints on the state changes that are allowed in a given state space. Such dynamic constraints can be seen as representations of "real world" constraints in a managerial context. The notions of transition, reversible and irreversible transition, and transition relation will be introduced. The link with Kripke models (for modal logics) is also made explicit. Several (subtle) examples of dynamic constraints will be given. Some important classes of dynamic constraints in a database context will be identified, e.g. various forms of cumulativity, non-decreasing values, constraints on initial and final values, life cycles, changing life cycles, and transition and constant dependencies. Several properties of these dependencies will be treated. For instance, it turns out that functional dependencies can be considered as "degenerated" transition dependencies. Also, the distinction between primary keys and alternate keys is reexamined, from a dynamic point of view

Unified management of multi-model data : (Vision paper)

Peer reviewe

Shrinking wings for ultrasonic pitch production: hyperintense ultra-short-wavelength calls in a new genus of neotropical katydids (Orthoptera: tettigoniidae)

This article reports the discovery of a new genus and three species of predaceous katydid (Insecta: Orthoptera) from Colombia and Ecuador in which males produce the highest frequency ultrasonic calling songs so far recorded from an arthropod. Male katydids sing by rubbing their wings together to attract distant females. Their song frequencies usually range from audio (5 kHz) to low ultrasonic (30 kHz). However, males of Supersonus spp. call females at 115 kHz, 125 kHz, and 150 kHz. Exceeding the human hearing range (50 Hz–20 kHz) by an order of magnitude, these insects also emit their ultrasound at unusually elevated sound pressure levels (SPL). In all three species these calls exceed 110 dB SPL rms re 20 µPa (at 15 cm). Males of Supersonus spp. have unusually reduced forewings (<0.5 mm2). Only the right wing radiates appreciable sound, the left bears the file and does not show a particular resonance. In contrast to most katydids, males of Supersonus spp. position and move their wings during sound production so that the concave aspect of the right wing, underlain by the insect dorsum, forms a contained cavity with sharp resonance. The observed high SPL at extreme carrier frequencies can be explained by wing anatomy, a resonant cavity with a membrane, and cuticle deformation

Natuurkwaliteit en biodiversiteit van de Nederlandse zoute wateren

Van de biodiversiteit in de Nederlandse zoute wateren is momenteel nog ongeveer 40% aanwezig van de biodiversiteit die zou bestaan in een oorspronkelijke, meer natuurlijke situatie. Deze conclusie is gebaseerd op een grote hoeveelheid gegevens over kenmerkende soorten en eigenschappen van de Nederlandse mariene ecosysteme

The Cercal Organ May Provide Singing Tettigoniids a Backup Sensory System for the Detection of Eavesdropping Bats

Conspicuous signals, such as the calling songs of tettigoniids, are intended to attract mates but may also unintentionally attract predators. Among them bats that listen to prey-generated sounds constitute a predation pressure for many acoustically communicating insects as well as frogs. As an adaptation to protect against bat predation many insect species evolved auditory sensitivity to bat-emitted echolocation signals. Recently, the European mouse-eared bat species Myotis myotis and M. blythii oxygnathus were found to eavesdrop on calling songs of the tettigoniid Tettigonia cantans. These gleaning bats emit rather faint echolocation signals when approaching prey and singing insects may have difficulty detecting acoustic predator-related signals. The aim of this study was to determine (1) if loud self-generated sound produced by European tettigoniids impairs the detection of pulsed ultrasound and (2) if wind-sensors on the cercal organ function as a sensory backup system for bat detection in tettigoniids. We addressed these questions by combining a behavioral approach to study the response of two European tettigoniid species to pulsed ultrasound, together with an electrophysiological approach to record the activity of wind-sensitive interneurons during real attacks of the European mouse-eared bat species Myotis myotis. Results showed that singing T. cantans males did not respond to sequences of ultrasound pulses, whereas singing T. viridissima did respond with predominantly brief song pauses when ultrasound pulses fell into silent intervals or were coincident with the production of soft hemi-syllables. This result, however, strongly depended on ambient temperature with a lower probability for song interruption observable at 21°C compared to 28°C. Using extracellular recordings, dorsal giant interneurons of tettigoniids were shown to fire regular bursts in response to attacking bats. Between the first response of wind-sensitive interneurons and contact, a mean time lag of 860 ms was found. This time interval corresponds to a bat-to-prey distance of ca. 72 cm. This result demonstrates the efficiency of the cercal system of tettigoniids in detecting attacking bats and suggests this sensory system to be particularly valuable for singing insects that are targeted by eavesdropping bats