Federal Highway Administration data from 2006 shows that 24.5 percent of the nation's bridges longer than 20 feet were categorized as "structurally deficient" or "functionally obsolete" (data from Utah and New Mexico was from 2005).
If the question was posed in more general terms, such as running experiments with deficient methods, failing to report deficiencies or misrepresenting data, the straight average suggested that 46% of researchers had seen others get up to such shenanigans.