Sharp (2008) wrote an essay critical of not only the Net Promoter Score but also of earlier work by Reichheld on customer defection, including the maxim that it costs five times more to attract than retain a new customer. He calls Reichheld’s claims about defection rates shockingly misleading.
Sharp then laid into Reichheld’s peddling of the myth of the NPS. He pointed out (as we, Grisaffe, and others have) the problem with using historical growth rates. He then called Reichheld’s work snake oil and fake science. This work was not peer-reviewed and it’s more of a commentary (or polemic). This paper was cited by Keiningham et al. (2015) as part of the “large body of evidence” refuting the NPS.
Takeaway: Sharp’s very critical essay of Reichheld raised the concern that historical growth rates can’t prove that the NPS is a leading indicator of growth.