UCD question: what UCD word to use for percentiles? stat.percentile proposal

[Mireille LOUYS]

Hi Bo , Hi semantics,

We have re-examined your use case together with S. Derriere and A. 
Preite Martinez and checked also how Vizier handles percentiles.

There is indeed currently no proper way to describe with UCDs that a 
measurement is associated to some percentile
of a statistical model/distribution.
Creating a new word could help describe these values :

Q stat.percentile    Percentile in a statistical distribution

We could also have a few more precise words to address exactly what you 
are trying to describe :

Q stat.percentile.1sigma    Percentile corresponding to one standard deviation from the median

Q stat.percentile.2sigma    Percentile corresponding to two standard deviations from the median


With these words, we could use :

ucd="src.redshift.phot;stat.percentile.2sigma;stat.min"  for EAZY  2.5% percentile of photo-z

ucd="src.redshift.phot;stat.percentile.1sigma;stat.min"  for EAZY  16% percentile of photo-z AND LePhare photo-z lower limit, 68% conf. level

ucd="src.redshift.phot;stat.median"  for EAZY  50% percentile of photo-z

ucd="src.redshift.phot;stat.percentile.1sigma;stat.max"  for EAZY  84% percentile of photo-z AND LePhare photo-z upper limit, 68% conf. level

ucd="src.redshift.phot;stat.percentile.2sigma;stat.max"  for EAZY  16% percentile of photo-z

In the UCD vocabulary, maybe an extra word would cover all possible cases :

Q stat.percentile.3sigma   Percentile corresponding to three standard deviations from the median

I hope this helps .
I have created a VEP-UCD for this term , and will circulate it in the 
UCD Board to discuss it for adoption .

Tell us wheter you can use this , and your feedback in case .
Thanks in advance .

Mireille & Sebastien
CDS, Strasbourg
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