Jared M. Spool wrote an article titled Net Promoter Score Considered Harmful.

Net Promoter Score (NPS) is calculated based on a one-question customer survey. “‘How likely are you to recommend [COMPANY] to a friend or colleague?’ On an eleven-point scale, with zero marked as Not At All Likely and 10 marked as Extremely Likely, respondents pick a number.”

“Any 9s or 10s are considered Promoters.
Any 7s or 8s are considered Passive respondents.
And any score from 6 to 0 is considered a Detractor.
The formula to calculate the score is:
Net Promoter Score = % of Promoter respondents minus % of Detractor respondents”

“For some reason, NPS thinks that a 6 should be equal to a 0. Nobody else thinks this.”

Spool calculates some hypothetical response data sets of ten respondents.

“0, 0, 1, 4, 5, 6, 7, 8, 9, and 10. The average… is 5. We would calculate the Net Promoter Score as 20% minus 60% or -40.”

“8, 8, 8, 8, 8, 8, 8, 8, 8, and 8. The average is 8. Yet, NPS is now… 0.”

“9, 9, 9, 9, 9, 9, 9, 9, 9, and 9. The average is 9. And miraculously, NPS is 100!
That’s 100% improvement over 8, so woohoo!”

“An eleven-point scale pretends noise is science.”

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