Availableonlineatwww.sciencedirect.col SCIENCE DIRECT. INFORMATION MANAGEMENT ELSEVIER Information Management 43(2006)127-141 www.elsevier.com/locate/dsw what do we know about mobile Internet adopters? a cluster analysis Shintaro okazaki Department of Finance and Marketing Research, College of Economics and Business Administration, Received 3 September 2004; received in revised form 8 March 2005; accepted 1 May 2005 Available online 16 june 200 Abstract consumers'attitude and their demographic characteristics have been only cursorily examined. The objective of our study was to fill this gap, by applying a two-step cluster analysis in profiling mobile Internet adopters in Japan. The findings suggest that four clusters exist: they exhibit distinct profile patterns. Paradoxical results were found within one, affluent single youth, which was further divided into two clusters: freelance, highly educated professionals had the most negative perception of mobile Internet adoption, whereas clerical office workers had the most positive perception. Married housewives and company executives also exhibited a positive attitude toward mobile Internet usage. C 2005 Elsevier B.V. All rights reserved Keywords: Mobile; Diffusion; Innovation; Internet: i-Mode; Japan; Uses and gratifications 1. Introduction number of Internet-connected PCs[44. Such dramatic convergence of the Internet and mobile telephony may In world markets, the rapid adoption of Web-enabled be attributed, in particular, to activity in Asian and mobile handsets has become increasingly important to Scandinavian countries, where penetration growth has Is professionals. A recent survey in 13 countries been meteoric. A recent survey indicated that roughly revealed an increase in usage of 145%0, reaching 79 70 million people in Japan(55% of the population)have million users in 2003, while the number of global signed up for Internet access from their cellular phone mobile Internet adopters has been predicted to reach compared with 12% of the population in the USA nearly 600 million by 2008 [19,35]. A pessimistic [13, 15]. In fact, the Japanese see cell phones or Keitai as forecast estimated that, by the year 2005, the number of devices for surfing the Internet while Americans use Internet-connected mobile phones would exceed the their laptops luch of this success can be traced to February 1999, when NTT DoCoMo, Japans leading mobile E-mailaddress:obarquitec(@coac.net. operator, launched the i-mode service. This isa mobile 0378-7206/S- see front matter 2005 Elsevier B V. All rights reserved doi:10.1016jm2005.05.001
What do we know about mobile Internet adopters? A cluster analysis Shintaro Okazaki * Department of Finance and Marketing Research, College of Economics and Business Administration, Autonomous University of Madrid, Cantoblanco, 28049 Madrid, Spain Received 3 September 2004; received in revised form 8 March 2005; accepted 1 May 2005 Available online 16 June 2005 Abstract Despite the increasing importance of wireless Internet use via Web-enabled mobile telephony, the relationship between consumers’ attitude and their demographic characteristics have been only cursorily examined. The objective of our study was to fill this gap, by applying a two-step cluster analysis in profiling mobile Internet adopters in Japan. The findings suggest that four clusters exist; they exhibit distinct profile patterns. Paradoxical results were found within one, affluent single youth, which was further divided into two clusters: freelance, highly educated professionals had the most negative perception of mobile Internet adoption, whereas clerical office workers had the most positive perception. Married housewives and company executives also exhibited a positive attitude toward mobile Internet usage. # 2005 Elsevier B.V. All rights reserved. Keywords: Mobile; Diffusion; Innovation; Internet; i-Mode; Japan; Uses and gratifications 1. Introduction In world markets, the rapid adoption of Web-enabled mobile handsets has become increasingly important to IS professionals. A recent survey in 13 countries revealed an increase in usage of 145%, reaching 79 million users in 2003, while the number of global mobile Internet adopters has been predicted to reach nearly 600 million by 2008 [19,35]. A pessimistic forecast estimated that, by the year 2005, the number of Internet-connected mobile phones would exceed the number of Internet-connected PCs [44]. Such dramatic convergence of the Internet and mobile telephony may be attributed, in particular, to activity in Asian and Scandinavian countries, where penetration growth has been meteoric. A recent survey indicated that roughly 70 million people in Japan (55% of the population) have signed up for Internet access from their cellular phones, compared with 12% of the population in the USA [13,15]. In fact, the Japanese see cell phones orKeitai as devices for surfing the Internet while Americans use their laptops. Much of this success can be traced to February 1999, when NTT DoCoMo, Japan’s leading mobile operator, launched the i-mode service. This is ‘a mobile www.elsevier.com/locate/dsw Information & Management 43 (2006) 127–141 * Tel.: +34 91 497 3552; fax: +34 91 802 0974. E-mail address: obarquitec@coac.net. 0378-7206/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.im.2005.05.001
S Okazaki/Information Management 43(2006)127-141 phone service offering continuous, always-on Internet Second, despite obvious cultural differences,an access based on packet-switching technology'[6]. empirical investigation of cons can serve as a Through a handset, users can access a micro-browser useful case study for other markets. DoCoMo's i-mode that offers services such as e-mail, data search, instant for example, has expanded to European countries; the messaging,Internet, and i-Imenu E-mail is considered adopters include E-Plus(Germany), KPN Mobile the most popular killer app, and 71% of i-mode users (Netherlands ), BASE (Belgium), Bouygues Telecon receive an e-mail newsletter [29, 38]. The i-menu acts( France), Telefonica Moviles( Spain), wind (Italy), and as a mobile portal resulting in approximately 4100 COSMOTE( Greece), and total subscribers reached 1.5 fficial and 50,000 unofficial sites offering diverse million by the end of 2003, from 270,000 at the end of additional functions 321 2002 [1]. The software platform and its content have One of the unusual features of i-mode is the way it been converted into added value resulting from the develops i-mode content. Instead of purchasing it, solution and partner network, possibly providing wider DoCoMo allows'designated third parties to provide implications [28]. Therefore, it is importan fee-based content and services with collection through a theoretical basis of the attitudes and demographics of the monthly phone bill. By October 2003, more than mobile Internet adopters 0 million subscribers to 2G and 3G i-mode Internet services existed. The key to understanding this growth lies in the profiles of mobile consumer segments but 3. Mobile content creation in the m-commerce little effort has addressed the fundamental question: value chain what are the attitudinal and demographic characte istics of mobile Internet adopters a chain of value-adding activities in The purpose of our study was to fill this gap, by commerce involves two global perspectives: conducting a two-step cluster analysis to identify and infrastructure-and-services [5]. The curren m ts of mobile Internet adopters in by global mobile players, however, pla ace more Our method overcomes the limitations of traditional strategic emphasis on content, the value chain of cluster analysis by: (1) considering both continuous content aggregation, its management, and access [25] and categorical variables and (2)automatically DoCoMo's i-mode, for example, is a ' semi-walled determining the number of clusters or segments on garden'controlled by its packet network and server the basis of objective statistical criteria. system; in this many different contents may be structured into official(approved) and unofficial(non- approved) providers(Fig. 1). However, only official 1gnilcance marge for content through DoCoMo's subscription billing system, which offers multiple .i. This study contributes to electronic commerce incentives for active content creation. literature in two ways. First, research on mobile The mobile portals play a key role in adding value to Internet adopters has primarily focused on the area of mobile market-making [5]. For instance, when users direct marketing: user profiles have rarely been select i-mode, they are presented with i-menu with links considered. The majority of the studies result from to personal information management applications, sporadic industry reports that leave an important offering users a one-stop shop solution. The increasing question unanswered: in developing effective busi- sophistication of mobile handsets has accommodated ness-to-consumer m-commerce strategies, how do diverse killer apps, such as built-in GPS, music information managers identify mobile Internet adop- downloads, videos, e-coupon for discounts. bill ters? And: what kind of demographic and psycho- payment, and even karaoke machines. Strategically, graphic segments do they have? An effort to classify this portal imposes no additional infrastructure costs, may therefore help in driving the development and number of third-party content providers and aggra e mobile Internet adopters based on specific attributes because the content creation can be arranged with execution of customer strategy and targeting of tors. As a result, in 2004 DoCoMo's group net profits more than tripled to 650 billion yen [2] and its
phone service offering continuous, always-on Internet access based on packet-switching technology’ [6]. Through a handset, users can access a micro-browser that offers services such as e-mail, data search, instant messaging, Internet, and i-menu. E-mail is considered the most popular killer app, and 71% of i-mode users receive an e-mail newsletter [29,38]. The i-menu acts as a mobile portal resulting in approximately 4100 official and 50,000 unofficial sites offering diverse additional functions [32]. One of the unusual features of i-mode is the way it develops i-mode content. Instead of purchasing it, DoCoMo allows ‘designated third parties to provide fee-based content and services with collection through the monthly phone bill’. By October 2003, more than 40 million subscribers to 2G and 3G i-mode Internet services existed. The key to understanding this growth lies in the profiles of mobile consumer segments but little effort has addressed the fundamental question: what are the attitudinal and demographic characteristics of mobile Internet adopters? The purpose of our study was to fill this gap, by conducting a two-step cluster analysis to identify specific segments of mobile Internet adopters in Japan. Our method overcomes the limitations of traditional cluster analysis by: (1) considering both continuous and categorical variables and (2) automatically determining the number of clusters or segments on the basis of objective statistical criteria. 2. Significance of the study This study contributes to electronic commerce literature in two ways. First, research on mobile Internet adopters has primarily focused on the area of direct marketing; user profiles have rarely been considered. The majority of the studies result from sporadic industry reports that leave an important question unanswered: in developing effective business-to-consumer m-commerce strategies, how do information managers identify mobile Internet adopters? And: what kind of demographic and psychographic segments do they have? An effort to classify mobile Internet adopters based on specific attributes may therefore help in driving the development and execution of customer strategy and targeting of customers. Second, despite obvious cultural differences, an empirical investigation of consumers can serve as a useful case study for other markets. DoCoMo’s i-mode, for example, has expanded to European countries; the adopters include E-Plus (Germany), KPN Mobile (Netherlands), BASE (Belgium), Bouygues Telecom (France), Telefonica Moviles (Spain), Wind (Italy), and COSMOTE (Greece), and total subscribers reached 1.5 million by the end of 2003, from 270,000 at the end of 2002 [1]. The software platform and its content have been converted into added value resulting from the solution and partner network, possibly providing wider implications[28]. Therefore, it is important to establish a theoretical basis of the attitudes and demographics of mobile Internet adopters. 3. Mobile content creation in the m-commerce value chain A chain of value-adding activities in mobilecommerce involves two global perspectives: content and infrastructure-and-services [5]. The current moves by global mobile players, however, place more strategic emphasis on content, the value chain of content aggregation, its management, and access [25]. DoCoMo’s i-mode, for example, is a ‘semi-walled garden’ controlled by its packet network and server system; in this many different contents may be structured into official (approved) and unofficial (nonapproved) providers (Fig. 1). However, only official providers can charge for content through DoCoMo’s subscription billing system, which offers multiple incentives for active content creation. The mobile portals play a key role in adding value to mobile market-making [5]. For instance, when users select i-mode, they are presented with i-menu with links to personal information management applications, offering users a one-stop shop solution. The increasing sophistication of mobile handsets has accommodated diverse killer apps, such as built-in GPS, music downloads, videos, e-coupons for discounts, bill payment, and even karaoke machines. Strategically, this portal imposes no additional infrastructure costs, because the content creation can be arranged with a number of third-party content providers and aggregators. As a result, in 2004 DoCoMo’s group net profits more than tripled to 650 billion yen [2] and its 128 S. Okazaki / Information & Management 43 (2006) 127–141
S. Okazaki/Information Management 43(2006)127-141 DoCoMo Network Provider Packet Radio tower i-mode server Unofficial Fig. 1. Functions of i-mode Internet service. Source: Reprinted by permission of Ref [28]- Table 1 Mobile Internet services in Japan Vodafone NTT DoCoMo Vodafone Au(KDDI Market share 60.5% 20.1% Number of subscribers 14.36 Markup language HDML 3G/2.5G network W-cdma Cdma2000 IX mum capacity(packet) 384 kbps er of official sites 50 >2000 1000 yen monthly charge 300 yen monthly charge 300 yen monthly charge +0.1 yen per packet +0.3 yen per packet +0.2 yen per packet In million [43]. Ref. [41 Refs.[17,32] d refs.[3,31,46 competitors, Vodafone and au(KDDI), implemented 4.1. Demographic profiling similar mobile Internet services. albeit using differe underlying technologies [17](Table 1) Demographic profiling is the process of the market by considering personal similarit differences, such as gender, age, marital 4. Profiling mobile Internet adopters occupation, monthly allowance, and household struc- ture. Such descriptive attributes have been used In pursuing this study, it was necessary to establish most industry surveys a conceptual framework for assessing the structure of Earlier industry reports have indicated that mobile the mobile Internet market. In general, markets consist Internet penetration was highest among young affluent of a number of segments, each of which is made up of males [42]. Most of them(83%)were found to use the natural groupings of customers[14]. Consumers can mobile Internet for personal purposes, but a sub- be split into different segments or clusters, within stantial portion (49%) also used it for work. WAP which customers have similar characteristics and adopters in Taiwan were predominantly young single needs [27]. The combined benefits were sought by males(21-40 years old) with middle income [18]. A adopting a two-step cluster analysis recent US industry report also indicated that a typical
competitors, Vodafone and au (KDDI), implemented similar mobile Internet services, albeit using different underlying technologies [17] (Table 1). 4. Profiling mobile Internet adopters In pursuing this study, it was necessary to establish a conceptual framework for assessing the structure of the mobile Internet market. In general, markets consist of a number of segments, each of which is made up of natural groupings of customers [14]. Consumers can be split into different segments or clusters, within which customers have similar characteristics and needs [27]. The combined benefits were sought by adopting a two-step cluster analysis. 4.1. Demographic profiling Demographic profiling is the process of splitting the market by considering personal similarities and differences, such as gender, age, marital status, occupation, monthly allowance, and household structure. Such descriptive attributes have been used in most industry surveys. Earlier industry reports have indicated that mobile Internet penetration was highest among young affluent males [42]. Most of them (83%) were found to use the mobile Internet for personal purposes, but a substantial portion (49%) also used it for work. WAP adopters in Taiwan were predominantly young single males (21–40 years old) with middle income [18]. A recent US industry report also indicated that a typical S. Okazaki / Information & Management 43 (2006) 127–141 129 Fig. 1. Functions of i-mode Internet service. Source: Reprinted by permission of Ref. [28]. Table 1 Mobile Internet services in Japan i-Mode Vodafone live EZweb Operator group NTT DoCoMo Vodafone Au (KDDI) Market share 60.5% 19.5% 20.1% Number of subscribersa 41.32 12.95 14.36 Markup language cHTML MML HDML 3G/2.5G networkb W-cdma W-cdma Cdma2000 1X Maximum capacity (packet)b 384 kbps 384 kbps 144 kbps Number of official sitesc 4100 650 >2000 Charged 1000 yen monthly charge + 0.1 yen per packet 300 yen monthly charge + 0.3 yen per packet 300 yen monthly charge + 0.2 yen per packet a In million [43]. b Ref. [41]. c Refs. [17,32]. d Refs. [3,31,46]
S Okazaki/Information Management 43(2006)127-141 user was male, between 18 and 34 years old, with a advantage over the idea it supersedes; (2)compatibility household income of uss 60,000 or more. Such with existing technology; (3)perceived complexity of findings suggest that the likelihood of adopting mobile its understanding and use;(4)trialability; (5)observa IT innovations is dependent on age and income, while bility to others. These variables collectively result in the effect of gender on mobile Internet service user attitude toward the mobile Internet, which in turn adoption remains uncertain. For example, a survey affects consumers' behavioral intent to use it of mobile text messaging by 500 British young adults Furthermore, prior research on Japanese i-mode found hardly any differences due to age or gender [7]. adoption suggested that the credibility of a new In addition, a survey of mobile banking adoption in communication channel was key to the choice of South Africa found that the majority(67%)of the access. This was important, because more than 20% of respondents were young, educated groups, either Japanese mobile Internet adopters accessed news and employed or studying or both, with the gender city guides, which often acted as a trusted information distribution approximately equal [9] source in their daily lives. Also, with logo branding sponsorship campaigns increasingly popul 4.2. Attitudinal profiling mobile sites, users may also have wanted to be sure of the trustworthiness of such paid-publicity. By choo While many industry surveys have focused on ing the i-menu, users could access a content-based descriptive characteristics, little diagnostic informa- platform, Tokusuru Menu(menu to your advantage, in tion has been provided on mobile Internet adopters, Japanese), which featured text banner ads from where similar demographic data may be differentiated sponsoring companies. By clicking, consumers could by the adopters'psychological motives. We therefore browse further detailed information pages that offered attempted to uncover profiles on the basis of: (1)the discounts, coupons, free-samples, sweepstakes, and uses and gratifications of adopters with the new media ring-tone downloads, etc. Therefore, in forming basic and (2)the diffusion of the mobile Internet as an attitudes toward and intention to access the mobile innovation Internet, individuals may have been reminded of the The uses and gratifications theory is axiomatic; it underlying information credibility and trustworthi argues that psychological needs shape an audiences ness adoption of the media [23]. This theory is primarily grounded on three basic tenets: media adopters are goal-directed, active media-users, and aware of their 5. Methodology needs. Because the mobile Internet service has been characterized as being highly personal, interactive, 5. 1. The questionnaire and immediate [10], important attributes can be found by profiling individuals according to the degree to Our study was part of an omnibus research project which they spontaneously perceive the medium to be conducted by an advertising research foundation in irritating, informative, or entertaining. These have Tokyo. The survey instrument included face, common been identified as principal motivations in wired and specific questions. The face questions covered Internet service adoption [11, 22, 24], while prior general demographic information, such as gender, research on the mobile Internet has made similar occupation, marital status, monthly allowance, and suggestions [4, 21) hours spent outside home. The common questions Rogers [36] defines the diffusion as 'the process by were related to general perceptions of media selection, which an innovation is communicated through certain leisure activity, consumption attitude, etc. Finally, the channels over time among the members of a social specific questions addressed attitudinal dimensions system. Therefore, it is a communication of new ideas, with respect to i-mode platforms, including content nich'participants create and share information with and source credibility, informativeness, entertainment, one another in order to reach a mutual understanding,. irritation, general liking, and willingness to access Thus, the mobile Internet seems to satisfy the five emed re asonable to assume that usage of e-mail principal characteristics of innovation:(1)relative messaging and access to mobile portals were two key
user was male, between 18 and 34 years old, with a household income of US$ 60,000 or more. Such findings suggest that the likelihood of adopting mobile IT innovations is dependent on age and income, while the effect of gender on mobile Internet service adoption remains uncertain. For example, a survey of mobile text messaging by 500 British young adults found hardly any differences due to age or gender [7]. In addition, a survey of mobile banking adoption in South Africa found that the majority (67%) of the respondents were ‘young, educated groups, either employed or studying or both’, with the gender distribution approximately equal [9]. 4.2. Attitudinal profiling While many industry surveys have focused on descriptive characteristics, little diagnostic information has been provided on mobile Internet adopters, where similar demographic data may be differentiated by the adopters’ psychological motives. We therefore attempted to uncover profiles on the basis of: (1) the uses and gratifications of adopters with the new media and (2) the diffusion of the mobile Internet as an innovation. The uses and gratifications theory is axiomatic; it argues that psychological needs shape an audiences’ adoption of the media [23]. This theory is primarily grounded on three basic tenets: media adopters are goal-directed, active media-users, and aware of their needs. Because the mobile Internet service has been characterized as being highly personal, interactive, and immediate [10], important attributes can be found by profiling individuals according to the degree to which they spontaneously perceive the medium to be irritating, informative, or entertaining. These have been identified as principal motivations in wired Internet service adoption [11,22,24], while prior research on the mobile Internet has made similar suggestions [4,21]. Rogers [36] defines the diffusion as ‘the process by which an innovation is communicated through certain channels over time among the members of a social system’. Therefore, it is a communication of new ideas, in which ‘participants create and share information with one another in order to reach a mutual understanding’. Thus, the mobile Internet seems to satisfy the five principal characteristics of innovation: (1) relative advantage over the idea it supersedes; (2) compatibility with existing technology; (3) perceived complexity of its understanding and use; (4) trialability; (5) observability to others. These variables collectively result in user attitude toward the mobile Internet, which in turn affects consumers’ behavioral intent to use it. Furthermore, prior research on Japanese i-mode adoption suggested that the credibility of a new communication channel was key to the choice of access. This was important, because more than 20% of Japanese mobile Internet adopters accessed news and city guides, which often acted as a trusted information source in their daily lives. Also, with logo branding and sponsorship campaigns increasingly popular in mobile sites, users may also have wanted to be sure of the trustworthiness of such paid-publicity. By choosing the i-menu, users could access a content-based platform, Tokusuru Menu (menu to your advantage, in Japanese), which featured text banner ads from sponsoring companies. By clicking, consumers could browse further detailed information pages that offered discounts, coupons, free-samples, sweepstakes, and ring-tone downloads, etc. Therefore, in forming basic attitudes toward and intention to access the mobile Internet, individuals may have been reminded of the underlying information credibility and trustworthiness. 5. Methodology 5.1. The questionnaire Our study was part of an omnibus research project conducted by an advertising research foundation in Tokyo. The survey instrument included face, common, and specific questions. The face questions covered general demographic information, such as gender, occupation, marital status, monthly allowance, and hours spent outside home. The common questions were related to general perceptions of media selection, leisure activity, consumption attitude, etc. Finally, the specific questions addressed attitudinal dimensions with respect to i-mode platforms, including content and source credibility, informativeness, entertainment, irritation, general liking, and willingness to access. It seemed reasonable to assume that usage of e-mail messaging and access to mobile portals were two key 130 S. Okazaki / Information & Management 43 (2006) 127–141
S. Okazaki/Infonnation Management 43(2006)127-14 indicators of mobile Internet adopters. Therefore In the first step, original cases are grouped into photographic images of i-menu portal sites were preclusters that are then used in place of the raw data nserted in the questionnaire in asking respondents for in the hierarchical clustering Based upon its similarity their general opinions on the use of such services. to existing preclusters, each successive case is added With regard to e-mail usage, the questionnaire to form a new precluster, using a likelihood distance included a filtering question: did respondents use e- measure as the similarity criterion. Cases are assigned mail messaging via mobile telephony? to the precluster that maximizes a log-likelihood function. In the second step, the preclusters are 5.2. sample grouped using the standard agglomerative clustering algorithm, producing a range of solutions, which is The sample involved stratified random sampling then reduced to the best number of clusters on the basis according to age and gender distribution. The popula- of Schwarz's Bayesian inference criterion BIC) tion was based on the Citizens Registry Book of the which is known as one of the most useful and objective Tokyo Metropolitan District. Questionnaires were selection criteria, because it essentially avoids the distributed to 1623 residents in the greater Tokyo area. arbitrariness in traditional clustering techniques. In A professional marketing organization was employed addition, both background noise and outliers can be for this task, and researchers visited each respondent to identified and screened out. leave the questionnaire. A total of 786 responses were collected in the next month, giving an effective response 6.2. Categorical and continuous variables rate of 48.4%. However, only 612 responses were included in the data analysis: those who regularly used ne categorical and continuous variables are shown the e-mail message service via the mobile phone in Tables 2 and 3, respectively. The categorical vari- ables involve gender, age, marital status, occupation, monthly allowance, and household structure. Monthly 6. Statistical treatment allowance was chosen over monthly income, on the assumption that the level of mobile usage expenditure is 6.1. The two-step cluster analysis a function of disposable allowance rather than of total income. Each variable was assessed on a categorical Traditionally, cluster analysis has been used for scale with no multiple responses allowed. The conti empirical classification of objects [16]. It is an explo- nuous variables were associated with general percep- ratory technique that has been widely applied in diverse tions of the mobile platform: content credibility, source ciplines credibility, informativeness, entertainment, irritation, and Ghose[8]applied a latent class modeling approach general liking, and willingness to access Each measure to segment Web shoppers based on demographics and consisted of a multiple-item scale, as indicated benefit sought while Jih and Lee [20] attempted to Table 3 segment cellular phone users according to their retail To ensure the adequacy of the selected variables, two shopping motives. Thus, this technique was deemed preliminary analyses were conducted in an attempt to appropriate in forming groups according to the simi- identify significant differences between mobile e-mail larity of their demographic and attitudinal variables users and non-users. This was needed because if there Our study used a statistical program, TwoStep were no significant differences between the two groups, Cluster in SPSS 12.0; this had been suggested as then profiling made little sense. First, the Pearson chi appropriate in clustering large data sets with mixed se square test was performed for each of the the categoric attributes [30]. The method is based on a distance variables across the two groups. The expected values in measure that enables data with both continuous and each cell were greater than 1 and most cells had categorical attributes to be clustered. This is derived expected values greater than 5. Significant differences from a probabilistic model in which the distance were detected at P<0.00l for all variables between e between two clusters is equivalent to the decrease in mail users and non-users. Second, a MANOVA was log-likelihood function as a result of merging [12] conducted with type of use or non-use as independent
indicators of mobile Internet adopters. Therefore, photographic images of i-menu portal sites were inserted in the questionnaire in asking respondents for their general opinions on the use of such services. With regard to e-mail usage, the questionnaire included a filtering question: did respondents use email messaging via mobile telephony? 5.2. Sample The sample involved stratified random sampling according to age and gender distribution. The population was based on the Citizens Registry Book of the Tokyo Metropolitan District. Questionnaires were distributed to 1623 residents in the greater Tokyo area. A professional marketing organization was employed for this task, and researchers visited each respondent to leave the questionnaire. A total of 786 responses were collected in the next month, giving an effective response rate of 48.4%. However, only 612 responses were included in the data analysis: those who regularly used the e-mail message service via the mobile phone. 6. Statistical treatment 6.1. The two-step cluster analysis Traditionally, cluster analysis has been used for empirical classification of objects [16]. It is an exploratory technique that has been widely applied in diverse disciplines for its partitioning ability; e.g., Bhatnager and Ghose [8] applied a latent class modeling approach to segment Web shoppers based on demographics and benefit sought while Jih and Lee [20] attempted to segment cellular phone users according to their retail shopping motives. Thus, this technique was deemed appropriate in forming groups according to the similarity of their demographic and attitudinal variables. Our study used a statistical program, TwoStep Cluster in SPSS 12.0; this had been suggested as appropriate in clustering large data sets with mixed attributes [30]. The method is based on a distance measure that enables data with both continuous and categorical attributes to be clustered. This is derived from a probabilistic model in which the distance between two clusters is equivalent to the decrease in log-likelihood function as a result of merging [12]. In the first step, original cases are grouped into preclusters that are then used in place of the raw data in the hierarchical clustering. Based upon its similarity to existing preclusters, each successive case is added to form a new precluster, using a likelihood distance measure as the similarity criterion. Cases are assigned to the precluster that maximizes a log-likelihood function. In the second step, the preclusters are grouped using the standard agglomerative clustering algorithm, producing a range of solutions, which is then reduced to the best number of clusters on the basis of Schwarz’s Bayesian inference criterion (BIC), which is known as one of the most useful and objective selection criteria, because it essentially avoids the arbitrariness in traditional clustering techniques. In addition, both background noise and outliers can be identified and screened out. 6.2. Categorical and continuous variables The categorical and continuous variables are shown in Tables 2 and 3, respectively. The categorical variables involve gender, age, marital status, occupation, monthly allowance, and household structure. Monthly allowance was chosen over monthly income, on the assumption that the level of mobile usage expenditure is a function of disposable allowance rather than of total income. Each variable was assessed on a categorical scale with no multiple responses allowed. The continuous variables were associated with general perceptions of the mobile platform: content credibility, source credibility, informativeness, entertainment, irritation, general liking, and willingness to access. Each measure consisted of a multiple-item scale, as indicated in Table 3. To ensure the adequacy of the selected variables, two preliminary analyses were conducted in an attempt to identify significant differences between mobile e-mail users and non-users. This was needed because, if there were no significant differences between the two groups, then profiling made little sense. First, the Pearson chisquare test was performed for each of the categorical variables across the two groups. The expected values in each cell were greater than 1 and most cells had expected values greater than 5. Significant differences were detected at P < 0.001 for all variables between email users and non-users. Second, a MANOVA was conducted with type of use or non-use as independent S. Okazaki / Information & Management 43 (2006) 127–141 131