Dynamic Heterogeneous Choice Heuristics: A Bayesian Hidden Markov Mixture Model Approach

김진교 서울대학교 경영연구소 2013 Seoul Journal of Business Vol.19 No.1

Standard choice models implicitly assume that consumers, in order to maximize their expected utilities, compare each of the alternatives in their choice sets in terms of all available attributes. Consumer-level utility functions are frequently taken as linear, and overwhelmingly so as compensatory. However, due to limitations in information process capacity,characteristics of choice task environment and other internal or external constraints, consumers may search for satisfying alternatives rather than optimal ones by invoking other non-compensatory heuristics which free them from arduous attribute-by-attribute comparison. The question arises as to how often these non-compensatory rules are applied, and whether researchers can detect them using only standard data sources. This study aims to address two main issues regarding consumers’ use of decision-rules and heuristics in the real world: (1) whether they are heterogeneous across consumers and (2) whether they are changing for individual consumers over time. To these ends, we extend the standard linear compensatory rule assumption to more faithfully capture dynamic heuristic usage for each consumer. There are three reference heuristics studied in this paper, the well-known linear compensatory, disjunctive and conjunctive rules. Conditional on this known set of possible heuristics, a dynamic heterogeneous hidden Markov mixture choice model is developed to capture heuristic dynamics at the individual-level. When estimated on detergent scanner data, the proposed model offers strong evidence supporting both heterogeneity and dynamics in heuristics usage.

Synchrotron X-ray scattering analysis of interfaces and nanostructures

김진교 한국진공학회 2007 한국진공학회 학술발표회초록집 Vol.16 No.2

Migration-Assisted Formation of GaN Nanodisks by Hydride Vapor-Phase Epitaxy

김진교,이상화 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.3

GaN nanodisks, which can be used as nanoscale dielectric resonators for compact photonic nanodevices, were grown by using hydride vapor-phase epitaxy with growth interruption. Growth interruption enhanced surface migration of species and controlled growth interruption allowed the formation of GaN nanodisks at a growth temperature of 1050 ℃ and even at a growth temperature as low as 510 ℃.

Branching Characteristics of GaN Multipods Grown by Using Hydride Vapor Phase Epitaxy

김진교,Yuri Sohn 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.3

GaN multipods were grown on c-plane sapphire substrates by using hydride vapor phase epitaxy (HVPE) and their branching characteristics were investigated by utilizing scanning electron microscopy. A catalyst-free vapor-solid growth mechanism gave rise to diversity in the formation of multipods in various structures. We found that the core structure primarily determined the branching configuration of the sideward GaN nanorods. Depending on whether the core had a zincblende structure or wurtzite structure, either 3-fold symmetric multipods without a vertical nanorod or 6-fold multipods were favorably grown.

Effect of the Temperature Gradient Between a Substrate and its Ambient on the Growth of Vertically-Aligned GaN Nanorods

김진교,Yuri Sohn,이상화,최혁민 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2

In a hot-wall reactor for hydride vapor phase epitaxy (HVPE), the substrate holder was specially designed in such a way that the substrate temperature was much lower than its ambient because of an additional cooling mechanism, and GaN nanorods were grown on these air-cooled substrates. From these experiments, both the substrate temperature itself and the temperature gradient between the substrate and its ambient were found to be critical parameters in the growth of GaN nanorods. In addition, synchrotron X-ray scattering revealed that the GaN nanorods did not contain the cubic phase commonly observed in GaN films grown at low temperatures.

Identifying Subject-Specific Relevant Explanatory Variables in Choice-Based Conjoint Studies

김진교 서울대학교 경영연구소 2013 Seoul Journal of Business Vol.19 No.1

It is customary in conjoint studies to introduce the same set of potential explanatory variables for each subject, so as best to allow any possible trade-offs to be made. However, this presumption can mask the possibility of some subjects’ considering only a subset of the presented attributes. Moreover, such subsets of relevant attributes can vary considerably across the population. This paper presents a model which allows researchers to identify relevant explanatory variables for each subject separately. This is accomplished via a solution to the well-known variable selection problem in the context of discrete choice models; the proposed solution can be widely applied throughout choice studies and in fact to other response types, such as ratings, direct paired comparisons, and ranks, with appropriate changes in likelihood function. When estimated on a choice-based conjoint data for dial-readout scale products, the proposed model is strongly preferred to the traditional random-effect specification for choice-based conjoint. A sizeable group of subjects, approximately 63%, were found to consider proper subsets of all attributes presented. There was a great deal of heterogeneity in attributes deemed relevant across subjects: the proportion of subjects who did not consider a given attribute among the six used in the study ranged from 17.4% to 41.3%. For those who did consider a given attribute, estimated attribute level part-worths were essentially identical for the proposed model and the traditional random-effect conjoint model; but this was not the case for non-considered attributes. In fact, the traditional model was found to suffer from systematic biases in aggregate part-worth magnitudes. Finally,and most important for marketing practice, allowing for the possibility that some subject may not consider particular attributes can lead to substantial design and revenue differences in supposedly ‘optimal’ products, at both the individual- and the aggregate-level.

Social Network를 활용한 마케팅

김진교 한국마케팅연구원 2008 마케팅 Vol.42 No.2

범주자료를 이용한 포지셔닝 맵

김진교 한국경영학회 2007 한국경영학회 통합학술발표논문집 Vol.2007 No.8

포지셔닝 맵은 가장 널리 쓰이는 마케팅 분석 툴 중 하나이다. 요인분석, MDS, 판별분석이 포지셔닝 맵을 위한 전통적 방법으로써 제안되었는데, 이중에서도 요인분석이 가장 우수한 방법으로 여겨져 왔다. 그러나, 요인분석과 판별분석의 경우 응답자로부터 여러 개의 속성 각각에 대한 점수를 비교대안 별로 수집하여야 한다는 측면에서, 응답부하가 크다는 단점이 있다. 이와 같은 응답부하 문제 때문에, 현재 국내,외를 불문하고 요인분석은 널리 활용되지 못하고, 속성별 범주자료를 이용하는 MCA가 최근 많이 활용되고 있다. MCA의 경우 주어진 특정 속성에 대한 설명과 부합되는 대안만을 선택하도록 응답을 받는 범주자료를 이용한다는 점에서 응답부하 측면에서 장점이 있다. 그러나, (i) 차원의 해석이 거의 불가능하며, (ii) 선호회귀분석 등의 중요 분석의 수행이 불가능하며, 가장 결정적으로는 (iii) 응답자별로 상품대안의 위치를 파악하지 못한다는 약점이 있다. 본 연구에서는 범주형 자료를 이용하면서도 위에서 언급한 MCA의 세 약점을 극복한 새로운 형태의 포지셔닝 맵 모형을 제안하다. 모형의 기본 구조는 다변량 프로빗 모형이다. 모형의 구조와 추정, 그리고 국내 SUV 시장에 대한 실제 적용 예 또한 살펴본다.

Transformation of In Grains to InN Nanoshells with In_2O_3 as an Intermediate State under a N_2-NH_3 Ambient

김진교,정인희 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.1

InN nanoshells were fabricated by using nitridation of In grains sputtered on sapphire substrates. The X-ray diffraction intensities of the sputtered In grains measured before and after nitridation show that In grains were seemingly transformed directly to InN, but further microstructural analysis revealed that the transformation of In to InN involved In_2O_3 as an intermediate phase. Our result illustrates that the oxidation of the In grains at low temperatures was more favored than the nitridation process and that the fabrication of InN from the pure In grains under an atmospheric thermal process might inevitably follow this two-step pathway.

내향중앙성과 외향중앙성이 상품선택에 미치는 효과에 관한 비모수적 반응표면분석

김진교(Jin Gyo Kim) 한국마케팅학회 2013 마케팅연구 Vol.28 No.2

상품에 대한 고객들의 구매네트워크는 고객 간의 커뮤니케이션 네트워크를 기반으로 하여 존재한다. 본 연구에서는 커뮤니케이션 네트워크와 구매네트 간의 상호의존성과 관련하여, 커뮤니케이션 네트워크 상 고객의 내향중앙성과 외향중앙성이 다른 고객으로 하여금 특정 상품을 선택, 구매함에 있어서 얼마나 영향을 주는지 그리고 어떠한 형태로 영향을 주는지를 비모수적인 방법인 다변량 적응회귀스플라인모형(MARS)을 사용하여 실증적으로 검토하였다. MARS모형의 추정결과, 내향중앙성과 외향중앙성 모두 상품의 선택확률에 유의적인 영향을 비선형적으로 준다는 것, 선택확률에 대한 내향중앙성과 외향중앙성의 효과가 위로 볼록하다는 것, 그리고 선택확률을 최대화시키는 내향중앙성과 외향중앙성의 최적 조합이 존재한다는 것을 발견하였다. One of the most important research questions in social network analysis is to capture, or predict, differences in tie strengths across node pairs. In a majority of marketing-based networks, multiple relations between nodes are not independent from one another. For example, aside from their core communication services, mobile phone service providers provide their customers with various extra products or services, such as mobile phone games, MP3 songs, and e-books. Since these extra products or services may proliferate via communication network among mobile phone users, it is critical to understand interwoven structures between communication and purchase networks. A growing body of studies in marketing has applied sociogram-based concepts and methods to investigate various issues of interrelationships among customers. None of these extant studies, has, thus far, examined interdependencies between communication relations and purchase relations. This paper aims to empirically investigate possible interdependencies between communication network and purchase networks. To this end, we measured indegree and outdegree centralities for each node in communication network and then rigorously investigated possible effects of the two centrality indices in communication network on their relations in purchase network on the basis of multivariate adaptive regression spline (MARS). In particular, degree centralities were measured for each pair of nodes in the communication network, as follows: where denotes connected (1) or disconnected (0) directed ties starting node and ending at node . Let denotes a binary observation for whether node made purchases (1) for a given product or service. Then, MARS model was fitted to data across all the possible pairs of nodes, as follows: where denotes probability of node making purchases for the product or service, is an unknown target function to be estimated, represents candidate explanatory variables for the directed tie , is the total number of hyperplanes, denotes the -th base spline function, and is the spline coefficient associated with . MARS model was fitted to real mobile phone usage data containing information about two particular types of relations among nodes: communications (i.e. phone call records) and purchases for a non-free extra service. Major findings attained from this particular application can be summarized as follows: First, both indegree and outdegree centralities were found to increase choice probabilities for the non-free extra service. Mobile phone users who might have relatively high scores for indegree and outdegree centralities would, therefore, exhibit relatively large influence on purchase decisions of those who were communicationally connected to them. Second, choice probability responses functions of indegree and outdegree centralities were not linear but nonlinear. These nonlinearities have been found by none of all the extant studies in the marketing literature, primarily because all of them have imposed linearity presumptions a priori on the effects of centralities on adoptions of information and/or products. Third, response surface of choice probabilities were not monotonically increasing but concave. Choice probabilities for the non-free extra service were, therefore, maximed at particular combinations of indegree and outdegree centrallities, rather than at maximum values of each of them. This last finding has not been reported by any of the extant studies in the marketing literature, mainly because they have failed in accounting for decisive possibilities that indegree and outdegree centralities might affect choice probabilities nonlinearly even with higher-order interaction effects.