Analysis of a special set of state court cases in 2000-01 from four jurisdictions in a study by the National Center for State Courts (Hannaford-Agor et al 2003) suggested that approximately 7% of the jury verdicts were wrongful convictions and 10% were wrongful acquittals, with corresponding rates of 10% wrongful convictions and 1% wrongful acquittals for the judges' verdicts (Spencer 2007).
Via the Legal Theory Blog.
The wrongful conviction rates in this study are pretty closely in tune with estimates from other sources (such as acquittals based on DNA evidence in murder-rape cases). Wrongful acquittal rates have been the subject of less overall examination, in part, because once there is an acquittal the bureacratic data set ends.
Also worth noting:
Virtually all of the pertinent studies since 1932 have pinpointed eyewitness misidentification as the single most pervasive factor in the conviction of the innocent.
From the article whose abstract appears here at footnote 79.