While there are good Budget Impact Analysis (BIA) guidelines, studies still register potential bias.
A study, published in Expert Review of Pharmacoeconomics & Outcomes Research, compared the results between theoretical and real-world evidence expenditures for medicines for hepatitis C: boceprevir and telaprevir. While both are not currently recommended in treatment guidelines following recent developments, this is an emblematic case because for 4 years these medicines consumed considerable resources.
The study demonstrated appreciable divergence between the theoretical budget impact and real-world evidence expenditures due to underestimated purchase prices and overestimated populations. The greater the degree of accuracy the more reliable and usable BIAs become for decision-making.
Full study results can be accessed here.