Hi Sara;
Without wanting to go into loads of detail on an email, your best place
to start is by reading Powell & Holland (1988), JMG 6, and Powell &
Holland (1994), Am Min 79.
"Sigma fit" is basically the scatter of the observed minus the
calculated enthalpis and activities normalised by their uncertainties.
"Hat" tells you how far a particular point lies from the centre of the
data spread i.e. the larger the number, the more influence on the result
it has.
Good luck!
Christian Walker
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