double-blind study - an experimental procedure in which neither the subjects of the experiment nor the persons administering the experiment know the critical aspects of the experiment; a double-blind procedure is used to guard against both experimenter bias and placebo effects.
No they get more expensive, airlines will always advise you to book in advance to take advantage of their best fares. Sometimes they do a special deal but not within a week of flying. I would try another airline or make different plans.
Christmas Eve is when it seems like everyone wants to travel and they tend to be very anxious and rude. The ticket price should be cheaper if you fly on the 25th and there is more chance there will be an available seat. out of the 2... christmas day would probably be cheaper.