Perhaps I can give some background on my understanding of those numbers.
I believe that the costing of the platform was based on the basic personal amount only. There are essentially three credits: the basic personal amount, the eligible dependant credit and the spousal amount, which are equivalent. If your spouse isn't working or you're a single parent, then you get, essentially, the basic personal amount. My understanding is that the costing was based on only the first of those, and the actual proposal includes all three.
In terms of the most recent Parliamentary Budget Officer costing, I think the difference is largely explained by a different database. The Parliamentary Budget Officer uses Statistics Canada's SPSD/M model, which basically takes some taxpayer information and some survey data and builds a model.
The department uses, essentially, taxpayer information. We use the tax returns filed by Canadians to build a microsimulation model, and that results in a more accurate, in our view, picture of the cost.