Have you created a font that has extra characters that can be used for statistics symbos?
Specifically, I’m looking for xbar (x with an overscore or line over it) used for the Mean
of a sample and and P-hat (upside down v over the letter p).
It seems that the characters are not included in Unicode, and I could not find them either. However, as suggested on this blog you can create them using combining diacritical marks.
My free fonts have the combining diacritics for what you need — combining overline, macron, and circumflex. This is Pāli.
Charis SIL has some smart font technology for better positioning of diacritics and should give good results in OpenOffice/LibreOffice.