Table 2.

Characteristics of test messages that Trial Promoter generated automatically for distribution on Twitter and Facebook.

Characteristic	Twitter	Facebook
Maximum message length limitation	Limitation to 140 charactersa	N/Ab
Parameter: URL	22 characters for non-https URLs 23 characters for https URLs	Links can be of any length. However, in order to simplify URL sharing and present clean URLs to the Facebook page visitor, Trial Promoter uses Bit.ly shortened URLs on Facebook posts as well.
Parameter: hashtags (disease keyword)	Yes (primary and if length permits secondary hashtag)	Yes (primary and secondary hashtags)
Parameter: link to official Keck Medicine of USCc Twitter account (@KeckMedUSC)	Yes	N/Ab

^aNote: Media attachments such as photos, videos, and polls are not counted toward 140 characters.

^bN/A: not applicable.

^cUSC: University of Southern California.