【正文】 ical about traditional panydriven advertising and marketing and increasingly prefer to make purchasing decisions largely independent of what panies tell them about products. This tectonic power shift toward consumers reflects the way people now make purchasing Once consumers make a decision to buy a product, they start with an initial consideration set of brands formed through product experience, remendations, or awarenessbuilding marketing. Those brands, and others, are actively evaluated as consumers gather product information from a variety of sources and decide which brand to purchase. Their postsales experience then informs their next purchasing decision. While word of mouth has different degrees of influence on consumers at each stage of this journey, it’s the only factor that ranks among the three biggest consumer influencers at every step. It’s also the most disruptive factor. Word of mouth can prompt a consumer to consider a brand or product in a way that incremental advertising spending simply cannot. It’s also not a onehit wonder. The right messages resonate and expand within interested works, affecting brand perceptions, purchase rates, and market share. The rise of online munities and munication has dramatically increased the potential for significant and farreaching momentum effects. In the mobilephone market, for example, we have observed that the passon rates for key positive and negative messages can increase a pany’s market share by as much as 10 percent or reduce it by 20 percent over a twoyear period, all other things being equal. This effect alone makes a case for more systematically investigating and managing word of mouth. Understanding word of mouth While word of mouth is undeniably plex and has a multitude of potential origins and motivations, we have identified three forms of word of mouth that marketers should understand: experiential, consequential, and intentional. Experiential Experiential word of mouth is the most mon and powerful form, typically accounting for 50 to 80 percent of wordofmouth activity in any given product category. It results from a consumer’s direct experience with a product or service, largely when that experience deviates from what’s expected. Consumers rarely plain about or praise a pany when they receive what they expect.) Complaints when airlines lose luggage are classic example of experiential word of mouth, which adversely affects brand sentiment and, ultimately, equity, reducing both receptiveness to traditional marketing and the effect of positive word of mouth from other sources. Positive word of mouth, on the other hand,can generate a tailwind for a product or service. Consequential Marketing activities also can trigger word of mouth. The most mon is what we call consequential word of mouth, which occurs when consumers directly exposed to traditional marketing campaigns pass on messages about them or brands they publicize. The impact of those messages on consumers is often stronger than the direct effect of advertisements, because marketing campaigns that trigger positive word of mouth have paratively higher campaign reach and influence. Marketers need to consider both the direct and the passon effects of word of mouth when determining the message and media mix that maximizes the return on their investments. Intentional A less mon form of word of mouth is intentional—for example, when marketers use celebrity endorsements to trigger positive buzz for product launches. Few panies invest in generating intentional word of mouth, partly because its effects are difficult to measure and because many marketers are unsure if they can successfully execute intentional word ofmouth campaigns. What marketers need for all three forms of word of mouth is a way to understand and measure its impact and financial ramifications, both good and bad. Wordofmouth equity A starting point has been to count the number of remendations and dissuasions for a given product. There’s an appealing power and simplicity to this approach, but also a challenge: it’s difficult for marketers to account for variability in the power of different kinds of wordofmouth messages. After all, a consumer is significantly more likely to buy a product as a result of a remendation made by a family member than by a stranger. These two kinds of remendations constitute a single message, yet the difference in their impact on the receiver’s behavior is immense. In fact, our research shows that a highimpact remendation—from a trusted friend conveying a relevant message, for example—is up to 50 times more likely to trigger a purchase tha