There are not that many ships that are comparable in both size and mission to what the government needs or plans on purchasing for polar icebreakers of that size. I think the only country that has ships that fit these two criteria is Russia and we didn't find there was sufficiently reliable data to use that as a basis for an estimate in the Canadian context.
Failing a perfectly comparable ship, we decided to go for another method of estimation, widely recognized as reliable, which is looking at both ships of comparable size even though they are not built for the same mission, and ships with a similar mission, but a different size, so polar icebreakers that are smaller.
By combining these two estimates, we arrive at an estimate for this type of ship and that size that is fairly reliable.
We also looked at the Canadian context to estimate costs in the Canadian context so historical data for ships that have been built, or are in the process of being built, in Canada, to take into consideration the Canadian costs, and design, acquisition and productivity differences for Canadian shipyards.