[Mister Underhill]

The original ballot that was sent out to the folks asked to vote lists the criteria:

AFI asks jurors to consider the following in their selection process:

CRITERIA

FEATURE-LENGTH FICTION FILM
Narrative format, typically over 60 minutes in length.

AMERICAN FILM
Motion picture with significant creative and/or production elements from
the United States.

CRITICAL RECOGNITION
Formal commendation in print, television and digital media.

MAJOR AWARD WINNER
Recognition from competitive events including awards from peer groups,
critics, guilds and major film festivals.

POPULARITY OVER TIME
Including success at the box office, television and cable airings, and
DVD/VHS sales and rentals.

HISTORICAL SIGNIFICANCE
A film's mark on the history of the moving image through visionary
narrative devices, technical innovation, or other groundbreaking
achievements.

CULTURAL IMPACT
A film's mark on American society in matters of style and substance.