It is based on an estimated 5% increase per year if the ACA had not gone into place. It's a guess.

It's a conservative guess.

Gabel and Smith analyzed data on rate increase filings for comprehensive health insurance products from a sample of states and found that individual market premiums grew by 11.7 percent in 2010, 7 percent in 2011, and 7.1 percent in 2012. A subsequent Assistant Secretary for Planning and Evaluation (ASPE) analysis by Rose Chu and Richard Kronick, also looking at public insurer rate filings to states, found that individual market premiums in 2013 grew by 7.9 percent in their data sample.

5% is a value that they choose since it the true value would've been more than that.

Now add on to that they are making the case that premiums are lower because of the extra charges based on gender, sickness, ext

That premiums are higher because of those.

It is interesting but it makes the assumption that the marketplace would be higher without the ACA.

It doesn't. It calculates that it is, using conservative assumptions.