How Many Amicus Briefs Were Filed In The Average Civil Case Between 2005 And 2020?

When we left off our study, one-third of the Supreme Court's civil cases were drawing at least one amicus brief.  In 2005, 27.08% of civil cases did.  That figure rose to 34.69% in 2006 before falling by nearly half but rose back to 31.58% in 2011 and 32.35% in 2013.  In 2017, 61.54% of the Court's civil cases had at least one amicus brief.  In 2018, 27.27% did.  In 2019, 41.18% did, and the share was 37.5% in 2020.

Appellants averaged one-third of an amicus brief per case in 2005.  After a one-year spike in 2006, that fell to 0.1463 in 2007 before rising to 0.3636 in 2010.  By 2012, appellants were averaging 0.425 briefs per case.  After a small dip, that rose to 0.4545 in 2015, 0.6154 in 2017 and 0.7647 in 2019.