How happy are people relative to neutral (as measured by experience sampling)?
I just finished reading this article (2018) by Michael Plant, a PhD student at Oxford University.  Given that it is not a peer-reviewed paper, it would be worth checking his references, but this is what he says about the neutral point:


  Life satisfaction surveys don’t ask people to specify what point on
  the 0 to 10 scale they would consider equivalent to not being alive. 0
  is labelled not at all’ and 10 ‘completely satisfied’. ... How could
  we settle where the neutral point is? Two strategies seem possible.
  First, we could find out at what LS scores individuals report their
  lives are neutral on experience measures of SWB. Second, we could poll
  people to ask at what LS score out of 10 they would be indifferent
  between living with that score for the rest of their life or dying. I
  am unaware of any analysis which has been conducted along either
  lines. Thus, for the moment, this unfortunately remains a point of
  armchair conjecture.


Note: LS = Life Satisfaction; SWB = Subjective Well-Being.