How long does someone need to live in NYC to be file as a full year resident?

I have read that living in NY for over 6 months would qualify someone as a full year resident. When I click this option for my wife, who was in NYC last year for 9 months, it increases the income we would receive back. It also allows us to EFILE, whereas indicating being a part year resident does not allow us to EFILE. Which should we choose to do?