This industry white paper assembles the economic case for air filtration against PRRSV. Two figures carry it: an approximately eightfold difference in outbreak risk without filtration, and 664 million dollars in annual PRRSV losses to US pork producers.
Both trace to peer reviewed sources that should be cited in its place. The eightfold figure comes from Dee and colleagues in 2012, where the odds of a new PRRSV infection before filtration were 7.97 times higher than after across 38 herds, with a p value below 0.01, and median time to new infection of 30 months in filtered herds against 11 months in non filtered. The 664 million dollar figure comes from Holtkamp and colleagues in 2013, and it is stated in 2011 dollars, which should be said whenever it is quoted as a present cost. The peer reviewed payback analysis is the financial companion to the Alonso 2013 work, reporting 2.1 years at 150 dollars per sow and 2.8 years at 200 dollars per sow.
The general point is about citation distance rather than about this document. An industry summary that reproduces a figure accurately is still one hop from the study, and each hop is a place where a qualifier can be dropped. The 7.97 odds ratio has a study design and a confidence level attached to it; rounded to eight and repeated without them, it becomes a slogan. For any figure that will support a capital decision, the primary paper is where the number and its conditions travel together.