  Social advertising uses information about consumers' peers, including peer
affiliations with a brand, product, organization, etc., to target ads and
contextualize their display. This approach can increase ad efficacy for two
main reasons: peers' affiliations reflect unobserved consumer characteristics,
which are correlated along the social network; and the inclusion of social cues
(i.e., peers' association with a brand) alongside ads affect responses via
social influence processes. For these reasons, responses may be increased when
multiple social signals are presented with ads, and when ads are affiliated
with peers who are strong, rather than weak, ties.
  We conduct two very large field experiments that identify the effect of
social cues on consumer responses to ads, measured in terms of ad clicks and
the formation of connections with the advertised entity. In the first
experiment, we randomize the number of social cues present in word-of-mouth
advertising, and measure how responses increase as a function of the number of
cues. The second experiment examines the effect of augmenting traditional ad
units with a minimal social cue (i.e., displaying a peer's affiliation below an
ad in light grey text). On average, this cue causes significant increases in ad
performance. Using a measurement of tie strength based on the total amount of
communication between subjects and their peers, we show that these influence
effects are greatest for strong ties. Our work has implications for ad
optimization, user interface design, and central questions in social science
research.
