CBO Director Douglas Elmendorf (AP photo/J. Scott Applewhite)

Repealing the Patient Protection and Affordable Care Act of 2010 (PPACA) might be more like trying to erase pencil marks with a bad eraser than like deleting text typed into a computer.

Douglas Elmendorf, director of the Congressional Budget Office (CBO), writes about the potential complications of analyzing the effects of PPACA repeal efforts today in a blog entry.

See also: PPACA costs fall as premiums beat forecast.

See also: CBO: We still think PPACA repeal would cost plenty.

The CBO is a think tank that helps members of Congress analyze budget proposals.

Elmendorf writes that members of Congress often ask the CBO to estimate the effects of changes to PPACA and of bills that would repeal part or all of PPACA.

Coming up with estimates that exclude the effects of PPACA — or any other federal legislation that’s already in effect — is more difficult than lawmakers realize, Elmendorf says.

“Whether a proposal to repeal the ACA specified alternative policies or not, its budgetary effects would not simply be the opposite of the budgetary effects of the ACA itself,” Elmendorf says.

Many “repeal” bills include few or no details about how federal agencies should go about reversing the effects of PPACA. Those bills would give the agencies “considerable discretion” in implementing repeal, Elmendorf says.

In some cases, he says, an agency could keep many of the same rules and procedures that it would have used if PPACA were still in effect.

In other cases, he says, an agency’s policies would have to change to something other than what was in place before PPACA came along because of the effects PPACA has already had on health care delivery or health care financing systems.