I'm not defending NPS. But your first and biggest argument in the article is unscientific and anti-statistical. You're making an emotional case that it looks weird because there are thresholds. You said "For some reason, NPS thinks that a 6 should be equal to a 0." and "Make that data set to be all nines: 9, 9, 9, 9, 9, 9, 9, 9, 9, and 9. The average is 9. And miraculously, NPS is 100!" Your reasoning here is faulty. You threw in sarcastic irrelevant comments about bonuses to make the idea of getting your NPS score wrong feel like it'll do damage.

Instead of investigating the possibly legitimate reason NPS people might be doing this, you put up a straw man argument about all respondents giving the same score. The likelihood of all respondents in a large survey all giving 8's is very, very close to zero. The likelihood of your NPS score suddenly flipping from 0 to 100 is very, very close to zero.

So you got my analogy and suggested an alternative, but you still don't see how probability of referral (or birth) is an indicator of business (or population) growth? You do seem to get it, so I don't understand what you're missing. I'm not sure how to (or if I need to) explain it better.

Polling a bunch of people how likely they are to refer a friend is like sampling the derivative of the growth function you want to estimate. If everyone responds accurately and tells the truth, and they refer people at the rate they said they would, you can use the data to predict your growth.

The fact that NPS puts the negative growth line at 60% says, to me, that they concluded that people inflate their self-reporting referral probabilities.

There is a mapping between what people report, and what they do. NPS might have the mapping wrong, but there is a mapping. I don't expect the NPS mapping to be very accurate, but if it's wrong I'd like to hear why. You haven't explained why it's wrong because you don't seem to understand why it might be right.

> Horrible analogy, but ok. I'd say, if there's any equivalent, it's asking how many people think they are likely they might get pregnant ever.

I don't understand what you're arguing (or why), you're splitting a very fine hair here, the difference between what you suggested and what I said is subtle at best. The NPS question is how probable are you to recommend this service to a friend. Someone with a low probability is likely to recommend to 0 friends. Someone with a (self reported) medium probability may be likely to refer 1 friend. Someone with a high probability may be likely to recommend 5 friends.

Asking a yes/no how likely one is to ever get pregnant would be a worse proxy for population growth than asking how many pregnancies you expect in your lifetime. The NPS question doesn't exactly ask either of those, it can be interpreted either way.

> They didn't do anything like that.

So what did they do? Your post ignores that question and argues it's purely bogus. I don't even know what they did, and I don't buy that NPS is pure fiction with nothing at all to back it. I totally would buy that the NPS scale was based on a small sample, and that it doesn't fit many companies very well.

> Like the earth is plausibly flat.

Not sure I get where the snark here is coming from. There exists an average response to this survey that is between 1 and 10 where below that number, statistically people will not refer anyone. What is that number? Why does 6 seem as plausible to you as the earth being flat?