Andrew Wilford explains for The Hill why it’s a bad idea to accept Congressional Budget Office estimates as gospel.

CBO is staffed with talented and hardworking professionals, but they are victims of budget scoring rules and institutional incentives that harm its ability to accurately provide a picture of the impact legislation will have on the budget. For example, CBO is prohibited from taking into account savings that arise from spending to combat waste. Front-end investments that yield back-end savings, thus, are bizarrely scored by as adding to the deficit rather than reducing it.

CBO’s structural problems have played a role in the passage of some significant legislation. For example, the Affordable Care Act (ACA) included an entitlement known as the CLASS Act, which was doomed from the start. However, it had one good thing going for it: the CBO’s budget scoring method. The agency uses a ten-year budget scoring window, but the legislation included a five-year vesting period, during which it would be collecting premiums but not paying out benefits. Not surprisingly, the resulting CBO score was favorable on paper. Fast forward two years to 2011, and the CLASS Act was quietly scrapped; an ignominious end to legislation that existed almost solely to make the ACA look more palatable to Americans concerned about the federal deficit.

Another area where CBO has come up short has been in its estimates of farm bills. Analysis in this area seems to be getting progressively worse, having underestimated the cost of the 2002 farm bill by $137 billion and the 2008 farm bill by $309 billion. The most recent legislation was sold with the promise of $16.5 billion in CBO-scored savings, driven by new commodity and disaster relief programs that were estimated to be $14.3 billion cheaper than the costly direct subsidy programs they replaced. Instead, these programs are actually on track to be more expensive than their predecessors.

Bill scoring isn’t the only place where CBO falls short of its goal. It consistently overestimates the effects of government spending on GDP growth, which was a major factor in missing the target on its estimate of the stimulus bill’s impact on employment.