According to Kaplan and Norton, good indicators are linked to cause and effect relationships. Reichheld does not attempt to demonstrate this himself, but there is ample literature on consumer behaviour that provides useful clues.5, 6
Involvement is a fundamental aspect of consumer behaviour, and low-involvement purchasing behaviour is utterly different from high-involvement purchasing. The vast majority of purchases are low-involvement and habit is often the guiding force for the consumer. These low involvement purchases by their nature don't generate WOM buzz and therefore Net Promoter can be ruled out as a useful measure on cause and effect grounds.
High-involvement purchases are items that are important to the purchaser and are closely tied to their ego and self-image. Cognitive activity and extended problem solving occur when the purchase is more involving and WOM is more likely. WOM, however, still has a peripheral impact even for high-involvement purchases.
There is extensive research on ‘where did you hear about our product’ collected by thousands of companies, and WOM seldom scores more than a few percent even in high-involvement product areas. Take, for example, pensions and motorcar purchasing, both of them high-involvement purchases. WOM is only a minor factor in pensions because the main source of advice is the Financial Advisor. The brand you choose is unlikely to coincide with dinner party chatter, even if you have a vocal acquaintance who talks about their pension — most people value the advice of their financial advisor more. In the case of motor vehicles, although people talk a lot about their cars and likes and dislikes, the final purchase decision is a highly personal one and more likely to be influenced by reviews in magazines or on television. Ask yourself, out of all the thousands of brands you have ever purchased in your entire life — clothes, shampoo, wrist watches, beer, insurance, car, cosmetics — what percentage of your brand and product choices were specifically copying one of your friends' choices of products and brands?
A very small number of examples are cited over and over again by WOM protagonists. For example, the popularity of the pop artist Lily Allen, who promoted herself via social networking rather than more traditional media. Yet this is precisely the type of ultra-high involvement purchase where WOM would be expected to be important, and as an example it's very unrepresentative of the other purchase categories.
Thus, cause and effect analysis of consumer behaviour indicates that (1) for most products and services there is little WOM and (2) even where WOM is more commonplace, people aren't necessarily influenced very much by it, except in very rare situations.