Just For Clicks: The Google Ad Model

2012年07月30日 07:20 AM

谷歌的廣告模式Just For Clicks: The Google Ad Model作者：英國《金融時報》專欄作家蒂姆•哈福德


When Hal Varian arrived at Google as a part-time economic adviser in 2002, he asked the then chief executive, Eric Sc​​hmidt, how he might make himself useful. Schmidt suggested that Varian might “take a look” at the way Google sold its advertising because “it might make us a little money”. That was an understatement: in 2011, Google's ad revenues were more than $36bn.
當2002年哈爾•瓦里安(Hal Varian)到谷歌(Google)擔任兼職經濟顧問時，他問時任首席執行官的埃里克•施密特(Eric Sc​​hmidt)他能發揮什麼作用。施密特建議瓦里安可以“看看”谷歌銷售廣告的方式，因為“它或許能讓我們賺點小錢”。這種說法可就太保守了：2011年谷歌的廣告收入超過360億美元。
Nice as it would be to give Varian all the credit for this - his textbook was my microeconomics bible - the foundation stones of Google's advertising success had been laid before he arrived. Traditionally, advertising is sold by salespeople who quote prices for advertisements. Google decided to auction advertising space instead. And when Varian, who is now Google's chief economist, took “a look” at the auctions that Google's computer scientists had designed, he found that they were pretty much perfect.
儘管瓦里安在其中有很大的功勞——他撰寫的教材可是我的微觀經濟學聖經，不過谷歌廣告的成功基石在他到來之前就奠定了。傳統廣告業是通過銷售人員為廣告報價來銷售。而谷歌決定把廣告空間拿來拍賣。當現在已經成為谷歌首席經濟學家的瓦里安“審視”谷歌計算機科學家們設計的拍賣機制時，他發現設計得相當完美。
If you search on Google, one set of Google computers tries to deliver the best possible search results; a second set is running an auction with the aim of delivering the most effective ads to be displayed alongside them, in 11 different positions of varying prominence. An auction is run every time a user searches - billions a day.
如果你用谷歌搜索，谷歌的一組計算機嘗試輸出可能的最佳搜索結果；另一組計算機則進行拍賣運算，目的是在搜索結果旁邊投放最有效的廣告，按重要程度不同共有11處廣告位置。用戶每搜索一次，拍賣就運行一次——每天多達數十億次。
Beyond the sheer computational demands, there are two reasons why these auctions are tricky to run well. First, these advertising spaces are substitutes for each other. If I sell flights to Reykjavik and you Google “flights to Iceland”, I want one of those ad spaces. I probably don't want all of them, and that might also irritate users, which is in the long-run interests of nobody (except possibly Yahoo and Microsoft, Google's rivals in this business).
除了海量的計算請求之外，這些拍賣運行起來相當棘手的原因有二。首先，這些廣告位置可以相互替代。如果我銷售飛往冰島首都雷克雅未克的航班機票，而你在谷歌搜索“飛冰島機票”，那麼我會想要一個廣告位置。我可能不需要全部位置，而且這樣做也會激怒用戶，從長遠來看對誰都沒好處（可能谷歌的競爭對手雅虎(Yahoo)和微軟(Microsoft)除外）。
Google doesn't want to sell slots in parallel because advertisers fear winning multiple redundant slots. The solution is something called a “generalised second price auction“: the winning bidder gets the top slot and pays whatever the second bidder offered; the second bidder gets slot two and pays the third-highest bid. (This is a slight oversimplification, as we shall see.) Google's willingness to accept less than each bidder actually offers might seem odd, but it encourages higher bids and may well raise more money overall.
谷歌不想一視同仁地出售廣告位，因為廣告主擔心會贏得多個冗餘位置。解決方法是一種稱為“廣義二階價格拍賣(generalised second price auction)”的算法：頭名中標者獲得第一廣告位，支付第二名競標者的報價；第二名中標者獲得第二廣告位，支付第三名競標者的報價。 （這麼說有些過於簡化，後面會看到。）谷歌願意接受比每位中標者實​​際報價低的價格看上去或許很奇怪，但這會鼓勵競標者報出較高的價格，從而很可能提高谷歌的總體收入。
The second problem is what the metric of bidding should actually be. Google could charge per “impression” - that is, for each time an advertisement is displayed. Or it could charge per “click” - each time a user clicks on the ad and travels to the advertiser's website. The difficulty here is that Google's costs - such as the forgone opportunity to sell space to someone else - are based on impressions, whereas the advertiser chiefly cares about clicks. I typed “Picasso prints” into Google and was offered the chance to buy some posters, but also to bid at an auction at Christie's. I'm sure Christie's gets far fewer clicks but is willing to pay much more for each of them.
第二個問題是用什麼作為競標的實際衡量標準。谷歌可以按照“展示”為單位收費，即一則廣告每展示一次就收一次費用；或者以“點擊”為單位收費，即用戶每點擊一次廣告跳轉到廣告主的網站就收一次費。這裡的困難在於，谷歌的成本（如放棄向其他人出售廣告位的機會）是按照“展示”次數計算的，而廣告主最關心的是點擊率。我在谷歌輸入“畢加索作品”，谷歌既向我提供關於購買招貼畫的搜索結果，也提供關於佳士得(Christie's)拍賣會的結果。我敢肯定，佳士得的點擊率會小得多，但它願意為每次點擊支付更高的價格。
Google's solution is to create a “quality” metric, largely based on expected clicks, that serves as an exchange rate between impressions and clicks. If Christie's is willing to pay $1,000 a click, and Google expects one such click, Art.co.uk will beat them with a bid of 10 cents a click, as long as Google expects more than 10,000 clicks - rightly so, since Google's expected revenue from Art.co.uk is higher. Art.co.uk will pay a sum related to Christie's bid and to the “quality” of both adverts.
谷歌的解決方案是根據預期點擊率創造一套“質量”標準，在展示和點擊之間起到“匯率”轉換的作用。如果佳士得願意為每次點擊支付1000美元，而谷歌預期它將獲得1次點擊，那麼，只要谷歌預期Art.co.uk的點擊次數會超過1萬次，Art.co.uk就可以憑每次點擊10美分的報價勝出——理應如此，因為谷歌預期從Art.co.uk將獲得更高的收入。 Art.co.uk支付的廣告費將取決於佳士得的報價和二者廣告的“質量”。
Despite the wrinkles, it is a simple idea, executed well. The biggest surprise for me is that many Google searches are “undersold”, with a few advertisers getting a bargain-basement rate - or no advertisers at all. Type “Hal Varian Google ad auctions” into Google and you'll see no ads. Type “flowers”​​ into Google and, I assure you, all 11 advertising spaces will be filled. It is on such searches that Google earns that $36bn.
這套方法非常絕妙，但很簡單，執行得也很好。令我最吃驚的是，谷歌的很多搜索結果是“低價出售的”，少數廣告主得以支付底價廣告費，有的搜索甚至完全沒有廣告。在谷歌輸入“Hal Varian Google ad auctions”，你看不到任何廣告。如果輸入“flowers”​​，我敢向你保證，全部11個廣告位都會被填滿。谷歌賺到的360億美元靠的正是這類搜索。

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