Efficiency Analysis for Display Ads and Contextual Search Yung-Ming Li Jhih-Hua Jhang-Li Institute of Information Management National Chiao Tung University, Taiwan Institute of Information Management National Chiao Tung University, Taiwan 886-3-5712121 Ext 57414 886-3-5712121 Ext 57340 [email protected] [email protected] ABSTRACT Most News Web sites provide display ads and contextual search, which are the main ad formats in Internet. Unlike display ads, Contextual search is a performance based advertisement and allows clients to bid for their exposure rate. Not only do Web sites save operation costs but also clients plan their budget flexibly. However, in addition to accuracy of search results, contextual search like a common resource pool will spend much more time to take the same number of clicks as display ads do. In this paper, we develop a simple economic model to examine the profitability and social efficiency of contextual search under monopolistic and duopolistic market structures. Keywords Display ads, Contextual search, Game theory, Pricing strategies, Competition question stems from the theatrical difference between pushing and pulling. Unlike traditional media pushing messages to individuals alternately in everyday life, people are active in Internet and pull information through this new medium, which means that audience have ability to read preferred content and avert their eyes from ad trap set by advertisers [19]. Consequently, click-thru rate (CTR), derived from dividing the number of visitors who clicked on an ad embedded in a web page by the number of times the web page was delivered, becomes an index for measuring the performance of advertisement. For example, Procter & Gamble, one of biggest advertisers in American, was the first company to contract with Yahoo to pay ad fee grounded on CTR in 1996. Since click behavior is useful to demonstrate online advertising effectiveness, the first attempt for modeling such effects over a relatively short period of time had been proposed by Chatterjee et al., which highlights the importance of explicit consumer identification procedures to enhance the value of clickstream data [6]. 1. INTRODUCTION The role of advertising is to deliver the message of individual products to consumers and higher exposure for a product means that it impresses more of the potential market [21]. According to “Internet Advertising Revenue Report” announced by IAB in 2006 April, Internet ad revenue in the United States amounted over $12.5 billion for the full year 2005, up from $9.6 billon reported in 2004. The increasing number suggests that Internet is one of most fundamental brand-building components in marketing platforms. The Internet ad formats can be divided into search, display-related advertising, and classifieds based on revenues ranked from high to low, accounting for more than 90 percent of revenues during these two years [9]. Because playing the role of content providers attracting different types of users, a News web site may carry display ads to offer clients more ways to reach their target audience and specific marketing objectives. By clicking a concerned hyperlink the clients may drive their potential customers to their web sites, enabling them to visit again after a few days. Traditional ad pricing strategy used in newspaper, radio, and television is based on cost per thousand, abbreviated as CPM, which means the cost for showing the ad to one thousand viewers. Web sites may guarantee an advertiser a certain number of impressions, an ambiguous term stamped on everyone’s mind; however, nobody can show whether it is worth the price to pay for the number of times an ad banner is seen by visitors. This Therefore, a new ad pricing mechanism plus contextual search has turned into the focus of attention because of a highly costeffective feature. The rule is simple: clients set their bid for each placement on sections or specific pages and only pay for a qualified click when a visitor clicks on their ads. In other words, clients can pay for performance and find their most valuable targets interested in the unique type of content a News web site offer. For each web page such program often represents three to five different ads in a frame, each including title, description, and display URL, whose size often corresponds to a large rectangle affording to place an independent display ad. The order of placement is determined by specific rules based on a combination of factors, such as relevancy, bid amount, click-thru rate, and so on. Because clients share a common resource pool, they have no ability to know when their ads appear on appointed web pages, but know that the chance of exposure decreases with the number of participants if more people enter the pool. Therefore, if time pressure caused by sharing is low or moderate, this seems a reasonable and economic way for advertisers to control their budget and implement their marketing plan in Internet. Because the expense to establish and maintain an online auction-based and pay-per-click platform is respectable, many News web sites cooperate with other firms which concentrate on search techniques to reduce their cost and take their profits from each page in pre-agreed proportions. The News web sites just copy and paste a block of JavaScript codes to their web page and then content-related ads start working without maintaining advertiser relationships. In addition to deliver relevant ads precisely targeted to the content, the mechanism may filter out improper and competitive ads. Like advertorials consumers trust, contextual search may have higher response rates than other web advertisements because it can provide useful information related to content for viewers. Thus, advertisers must be careful not to create a negative brand impression by causing consumers to feel deceived [17]. 2. Literature Review The effect advertising is mainly determined by ad expenditure level, time in market, number of competitors, and order of entry [22]. To expand the entire market and win market share, Bass et al. define advertising as “generic advertising” and “brand advertising” according to the effect of advertising, respectively. Their results suggest that generic and brand advertising must be properly coordinated for preventing suboptimal allocation of advertising budget [2]. Because media purchasing is the largest portion of advertising spending [14], a large number of mathematical models (e.g., game theatrical model, regression model and so on) had been proposed. Regarding the advertising strategies, Nguyen and Shi address the issue of optimal advertising strategies incorporating both market-share dynamics and market-size dynamics [16]. Shaffer and Zettelmeyer examine how the choice of advertising and the extent of ad exposure drive firms’ optimal strategies based on the Hotelling model of demand [20]. Saeed et al. highlight that advertising spending alone has only a negligible impact on firm performance; thus, companies should provide a better productownership experience to execute effective advertising policies [18]. Jedidi et al. measure the effects of changes in advertising and promotion policies on sales and profits, suggesting that advertising has a positive effect on “brand equity” in the long term [11]. Banerjee and Bandyopadhyay construct a multistage game theoretic model of advertising and price competition in a differentiated products duopoly, which exhibit that advertising spending by the large firm provides a positive externality on the small firm’s profits [1]. Because characterized by “two-way communication” and “conveying detained information”, Web is perceived to be very far from most of the other media [5]. Two-way communication, also known as interactivity, defined by Bezjian-Avery et al. et al. [3], turns Internet into a more efficient medium than traditional media for high involvement products [23]. Statistical data also suggest that Internet ads are more likely conducted by companies in the automotive-and-durables and financial-services sectors [15]. Advertisements provide a majority of revenue for advertisementsupported Web sets; however, increasing advertising may repels visitors [8]. Therefore, allocating ads efficiently becomes a solution to enhance revenue without hurting visitors’ feelings. For instance, a technique report shows that experts in Microsoft Research had developed an approach delivering banner advertisements efficiently on the msn.com Web site, running roughly 500 advertisements at a time [7]. Prior research suggests developing one common Web advertisement for all users may not be the most effective way to drive intended visitors to a certain web site [13]. One of the fundamental questions that marketers face in advertisement is how to implement target advertising to specific consumers and how to allocate their media budgets [10]. In the recent studies, Kim et al. use tree induction techniques and data-mining tools to generate marketing rules that match customer demographics, providing personalized advertisement selection when a customer visits an Internet store [12]. Bhatnagar and Papatla examine the issue of how to identify ideal paid advertising based on consumer search behavior. They assume that consumer interest in obtaining information on different categories can be represented by the locations of the categories on a search continuum in multidimensional space [4]. Similarly, we consider that the sections of News web sites also maintain the ability to classify particular visitors with the same interest. 3. Model We consider an ad pricing problem where clients want to publish their advertising on News web sites through two different platforms: display ads or contextual search. In our assumption, the advertising market of News web sites is dominated by a monopolistic firm or two firms competing against each other, which have the same traffic volume. For acquiring maximum profit, these firms determine which services they provide and make a proper pricing decision. We assume that each client has an adequate budget and carries individual ad on one News web site at most. Thus, let d denote the total number of clients buying display ads, and s the total number of clients buying contextual search. For the sake of analytical convenience, the market size is normalized to one, which means d s 1 . Furthermore, in this paper we consider that the most value of web advertising stems from the number of times visitors click on an ad; therefore, we omit “impression” utility in the following discussion. 3.1 Client utility functions To begin with, we assume that in the market News web sites have sufficient contents to serve all clients who want to publish their ads on the News web sites; in addition, based on traffic volume, these News websites claim that the expected number of times visitors click display ads in a unit time interval is N . Then, we denote as the “click” utility each client derives from using display ads in this unit time interval. Thus, a News web site may charge pd for display ads (e.g. a banner ad) for the fixed period. If a client pays pd to carry her ad on the News web site, everyone will touch it every time once they enter a specific web page containing it during the period. In contrast, News web sites providing contextual search may charge p for one-click. Therefore, in order to receive the “click” utility as the same as that received by clients using display ads, ones using contextual search must pay ps , where ps N p . In addition, the clients using contextual search must spend much more time to derive the same “click” utility than that using display ads because their ads appear alternatively and search results may not agree with contents. Therefore, a typical client i faces heterogeneous time cost wsi caused by s clients sharing the common resource pool when she carries advertisement through contextual search, where variable i stands for individual sensitivity on the value of time, and is uniformly distributed over an interval [0,1] . A client i with higher value of i has more time pressure than others whose levels of sensitivity are less than hers. The parameter w reflects the degree of relevancy search engine can achieve and decreases with the accuracy of relevant target content. The utility function of each client is given by pd Ui ps wsi def display ads (3.1) contextual search survive (i.e., positive profit) even if their competitors operating contextual search lower price to zero. 3.3 Monopolistic Market In a monopolistic market a firm operating News web site may choose to provide a single platform or hybrid platform. If only running display ads, the firm will set the price at , extracting all surplus of the clients. Each client accepts the price ( dm 1 ) and firm’s profit is dm cd . In contrast, if only offering contextual search, the firm will set the price at ws2 , and the profit function becomes 3.2 Platform demand functions In this section we consider three types of platform configuration: display ads, contextual search, and hybrid ads. First, if only display ads are provided, all clients pay ad fees as long as pd holds. Second, if only contextual search is provided, because the maximum value of i is equal to the total number of clients purchasing contextual search, clients Max sm w sm psm 2 m s won’t carry their ads through the platform. Thus, the demand Thus, firm’s profit is given by ps d m m s , ps w . Last, if both display ads and contextual search are offered, the marketsegmentation condition is given by p p w ˆ , s s where the utility with the index of time pressure ˆ a client derives is indifferent between these two services. Consequently, client i with ˆ will choose contextual search; otherwise, she select the d s where ˆ is given by , pd ps w 1, p ps ˆ d , 0 pd ps w w 0 , pd ps 0 s pd ps . w (3.5) 3 sm 2 4 27w . (3.6) Then we consider a hybrid platform, where price decisions of the two platforms are taken simultaneously by a monopolistic firm. Thus, the profit-maximization problem of the monopolistic provider is written as pdm psm w Max m pdm cd 1 m m d s pd , ps psm pdm psm w . (3.7) Since both demand functions of display ads and contextual search are associated with the difference of these two platform prices dividing by the accuracy of contextual search, denoted (3.2) as p pdm psm w , instead of solving the first order condition with respect to pdm and psm , we rewrite the objective function as Thus, the demand function of these two platforms are given by pd p s and d 1 w (3.4) 3w ,2 3 . i other platform. Let d and s denote the total number of clients who prefer to display ads and contextual search, respectively. The market share for ads can be derived from 1 ˆ and ˆ , 3 Solving sm sm 0 , the optimal price and market share for contextual search is given by with i2 ps w utilize contextual search and the others function of contextual search is given by s . sm w sm (3.3) Subsequently, we assume average marginal operations cost per client is cd for serving a client using display ads. For example, clients and editors of News web sites may discuss how to prepare adaptable content to fit for their ads. In contrast, because the workflow of contextual search is nearly automatic, the impact of the number of clients on variable cost is sufficient small ( cs 0 ), compared to display ads. Therefore, we assume that the variable cost of contextual search is zero. To ensure that the participation and incentive-compatible conditions hold, we assume that pd cd , pd ps , and cd . We also assume w cd such that firms maintaining display ads may Max dm s pdm cd 1 p pdm wp pdm , p p . (3.8) It can be easily observed that the joint profit is linearly increasing with pdm , and dm s is concave on p . Solving the first order condition dm s p 0 , the optimal price offset is given by pdm psm cd 3 , where p cd 3w . Then, the price of display ads pdm should be as high as possible such that the maximal profit is reached. Hence, the pricing schemes and corresponding market shares in the hybrid platform are given by m m s , ps m m d , pd c 1 d 3w , 3 cd 3 and cd 3w , , (3.9) yielding a total profit of dm s 1 5 cd w dc 4 1 5 2 cd . cd 1 3 3w (3.10) , (3.16) 3 sc c 2w 1 1 5 d 125 w , and dc more profit from a hybrid platform than a single one. (c) In a monopolistic market, the lowest allowable bid in a hybrid platform is larger than that in a single one. c 3w 1 1 5 d 125 w c d 5 c 4 1 5 d w 3.4 Duopolistic Market If the variable cost of display ads is very small cd 0 , profit In this section we examine the pricing scheme of ad platforms instituted by independent profit-seeking firms, which own and operate different ad platforms. The business environment for display ads and contextual search is largely determined by relative market power between these two firms. We consider three cases of market power distribution in non-cooperative pricing dynamics. In the first case both firms offering different platforms participate in a simultaneous Bertrand pricing competition game, each of which with symmetric market power. In the subsequent cases we consider a market structure that one of the firms gets the leadership of pricing decision; in other words, these two firms participate in a Stackelberg (leader-follower) pricing competition game. levels of both platforms can be simplified to Proposition 1. (Monopolistic market) (a) Contextual search will be more profitable than display ads for a monopolistic firm if the accuracy of contextual search is sufficiently high, where w 4 3 27 cd . (b) The monopolistic firm always makes 2 sc 2 c 4 1 5 d w (3.17) . (3.18) 16 36 w and dc w. 125 125 (3.19) Proposition 2. (Simultaneous price competition) (a) The market share of contextual search (display ads) increases (decrease) with the variable cost cd of display ads and the accuracy of search results. (b) If the variable cost cd of display ads is sufficient small, the profit level of display ads is larger than that of contextual search. 3.4.2 Sequential pricing competition 3.4.1 Simultaneous pricing competition In a simultaneous price competition environment, both firms maintaining different platforms attempt to create their maximal profit. Let d denote the profit function of display ads, and s the c c profit function of contextual search, respectively. Thus, the profit functions of these two firms are given by sc pscsc psc p psc c d w and (3.11) dc pdc cd dc pdc cd 1 p c d psc w . (3.12) . cd cd w 4 10 4 1 5 25 w w . (3.13) cd w , Solving first order condition of display ads directly yields the subgame perfect Nash equilibrium results as follows: c (3.14) (3.15) (3.20) where dcds 1 pdcds 3w . pdds Hence, market share and profit levels can be derived from using (3.3), which are given by 1 5 dcds pdcds cd dcds , cd cd w pdc 6 15 6 1 5 25 w w sc 1 1 5 response function of contextual search, pscds , and rewritten as Solving sc psc 0 and dc pdc 0 simultaneously yields equilibrium prices given by psc Instead of pricing simultaneously, we assume that which firm makes pricing decision first is dependent on its own market power. Therefore, we assume that the firm operating display ads offers a price first. Then, the firm operating contextual search makes its pricing decision after observing the offer. Thus, the best response function of contextual search to display ads is the same as that results from simultaneous decision, i.e., 2 cds cds cds ps R pd pd . Utilizing backward induction approach, 3 the profit function of display ads is given by plugging in the best 2 c w 1 1 d 3 w c 2w c , ps ds 1 1 d 9 w dcds 2 1 1 3 cd w c 1 c , s ds 1 1 d 3 w 1 9 cd w 2 c w 1 1 d 3cd , w dcds 2 1 , 2 (3.21) (3.22) (3.23) dependent on the accuracy of contextual search (the variable 3 c 2w 1 1 d . 27 w and scds (3.24) If the variable cost of display ads is very small cd 0 , then firms’ profit levels become scds 16 4 w and dcds w . 27 9 (3.25) Proposition 3. (Sequential pricing competition, display ads first) (a) Both the prices of these two platforms will increase with the variable cost cd of display ads and decrease with the accuracy of contextual search. (b) The market share of contextual search is larger than that of display ads. (c) The profit of contextual search is large than that of display ads if the variable cost cd of display ads is sufficient small. Next, we assume that the firm providing contextual search has market power, drawing up its pricing strategy first. Similarly, solving first order condition dcsd pdcsd 0 yields c pdsd c pcsd w s 1 1 3 d 9 w Max scsd pscsd scsd pscsd pscsd . csd 1 1 3 cd ps 3 w (e.g., p p csd s (3.26) . (3.27) ), and grabbing its clients. In other words, the firm maintaining contextual search may charge cd N for the lowest allowable bid per click to make maximal profit. Consequently, equilibrium price, market share, and the levels of profit are given by c pdsd cd 4 w , pscsd cd , 9 dcsd 1 3 , scsd 2 3 , dcsd 4 2 w , and scsd cd . 27 3 W d s U . (4.1) i 4.1 Monopolistic market First, consider a monopolistic firm operating and owning a single platform. Suppose that the monopolistic firm decides on either maintaining display ads or contextual search. Then, social welfares are given by Wdm cd , and m m 2 the firm providing contextual search should keep pscsd cd to preventing firm providing display ads from undercutting csd d In this section, we analyze the economic efficiency (social welfare) of different strategies adopted by firms in monopolistic and duopolistic markets, comparing them with socially optimal results. Social welfare of market is defined as summation of the firms’ profit and the clients’ surplus, which are given by m We find that scsd pscsd 0 always holds, which means that the profit level of contextual search increases with its price. However, c pdsd 4. Analysis of Economic Efficiency Ws ps s Hence, the profit maximization program of contextual search is given by pscsd cost cd of display ads). s (4.2) m 0 m m ps w s d 5w 2 3w 3 (4.3) Now suppose that a hybrid platform is offered by the monopolistic firm, the social welfare of which is given by m m m m m Wd s pd cd d p s s cd 5w 2 cd 3w s 0 m m m p s w s d (4.4) 3 4.2 Duopolistic market In a duopolistic market, the function of social welfare is given by Wd s pd cd d pd d ps s s 0 ps w s d cd w s 2 (4.5) 3 cd s . This equation implies that the social welfare of either simultaneous pricing competition or sequential pricing competition can be evaluated directly by market share of (3.28) contextual search and variable cost cd of display ads. Thus, the (3.29) social welfare gained with respect to different pricing strategies is derived as follows: (1) Simultaneous pricing competition (3.30) Proposition 4. (Sequential pricing competition, contextual search first) (a) The market share of contextual search is twice as much as that of display ads. (b) The price of display ads decreases with the accuracy of search engine while the price of contextual search keeps the same level as the variable cost cd of display ads. (c) The profit level of display ads (contextual search) is only Wdc s cd where sc w sc 2 3 cd sc , c 1 1 1 5 d 5 w . (2) Sequential pricing competition, display ads first (4.6) Wdcdss cd where scds w scds 3 cd scds , 2 c 1 1 1 d . 3 w . (4.7) w (3) Sequential pricing competition, contextual search first c Wd sds cd where scsd 3 w scsd cdscsd , 2 . (4.8) 2 . 3 4.3 Socially planned market In a socially planned market, social welfare of display ads alone and its socially optimal market share are given by Wdw cd and dw 1 , where cd pdw . (4.9) Similarly, social welfare of contextual search alone is given by Wsw pswsw sw sw 0 psw wsw d (4.10) 3 1 w sw 2 Solving first order condition Wsw sw 0 yields socially optimal market share, leading to pricing strategy and social welfare in a planned market, which are given by sw 2 2 , psw 3 , and Wsw w 3w 3w 3 , respectively. (4.11) Last, we consider a socially planned market providing both display ads and contextual search, the function of social welfare of which is given by Wdw s pdw cd dw pdw dw pswsw sw 0 psw w sw d cd 1 sw (4.12) 1 w sw 2 3 Socially optimal market share, the prices, and welfare of the market are derived from solving first order condition Wdw s sw 0 and using the demand functions (3.3), which are given by sw 2 2cd , pdw cd psw , and 3 3w 3 Wdw s 2c 2 cd w d , respectively. 3w market operating contextual search alone grabs more clients and charges less than a monopolistic market. (c) The social welfare of planned market (monopolistic market) providing contextual search alone is larger than that providing a hybrid platform when the accuracy of search results is sufficiently high, i.e., (4.13) Proposition 5. (Efficient platform allocation) (a) The excellent search technique is beneficial to social welfare in all markets if there exits a contextual search platform. (b) A centrally planned 8 1.5 c1.5 d 27 cd 2 2 (w 25 1.5 c1.5 d 108 cd 2 2 ). 5. Conclusions In this paper, we have developed an economic model to study the competence between display ads and contextual search in either monopolistic or duopolistic market. In a monopolistic market contextual search turns into a powerful weapon to make respectable revenue for firms concentrating on search technique, threatening the position of traditional display ads. However, in an integrated market contextual search can be used as a vertical product differentiation strategy to improve profit when the variable cost of display ads exists and the results of contextual search is not accurate enough. Comparing the profitability and social welfare with respect to pure strategies (display ads or contextual search) and hybrid strategy under monopolistic and social planned market, we suggest that hybrid strategy is better than pure strategy; however, maintaining contextual search alone is the best strategy if search technique is prominent. In duopolistic market, market share of contextual search ranges from 40% to 80% dependent on which pricing scheme is launched. It is noteworthy that the profit level of contextual search won’t increase with the quality of search engine when the variable cost of display ads is sufficiently small. This effect results from the fact that the firm maintaining display ads will lower price such that both firms’ profits are reduced. Comparing social welfare with respect to different pricing schemes, we find that when the ratio of the variable cost of display ads to the quality of contextual search is close to one, sequential pricing with contextual search first makes maximal social welfare in the market; however, if this ratio is close to zero, simultaneous pricing does. In our model we shed the “impression” utility and assume that the parameter representing the quality of contextual search is larger than the variable cost of display ads. However, if the case reverses and firms proving display ads alone survive in a competitive market, the “impression” utility should remain valuable for some particular clients such that these clients still purchase it. On the other hand, News web sites providing contextual search, in fact, manipulate a starting price that serves as both the lowest allowable bid and the minimum payment for one-click. For simplicity in our model we assume that each client exploiting contextual search pay the same price, equal to the lowest allowable price announced by a News web site. Therefore, if each client bids based on her budget and individual valuation, this question will relate to Vickrey auction; thus, it is an interesting topic for future research to study market share in the environment where the exposure rate of ads is determined by bid value. 6. REFERENCES [1] Banerjee, B. and Bandyopadhyay, S. Advertising Competition Under Consumer Inertia. Marketing Science, 22, 1 (2003), 131-144. [2] Bass, F. M., Krishnamoorthy, A., Prasad, A., and Sethi, S. P. Generic and Brand Advertising Strategies in a Dynamic duopoly. Marketing Science, 24, 4 (2005), 556-568. [3] Bezjian-Avery, A., Calder, B., and Iacobucci, D. 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