day of as many smartphone users
as possible. This would allow us to
catch all different types of users
(tech-savvy, elderly, left-handed,
etc.) and usage contexts (at night, in
traffic, during a bus ride, etc.). This
leaves us with the challenge that
testing all relevant situations will
often not be possible due to lack of
resources. Or, to put it differently,
how can a grad student recruit
thousands of participants from all
over the world and study them in all
the situations they face in daily life?
Mobile HCI Research in the Large
On July 10, 2008, Apple launched
the iOS App Store. It was the first
open unified distribution channel
for smartphone (iPhone) apps. The
App Store and similar stores, such
as Google Play and Windows Phone
Marketplace, dramatically lowered
the hurdles for developers. HCI
researchers realized that this could
extend the external validity of
research by allowing them to conduct studies with a diverse sample
of users and usage contexts.
Just as in traditional studies,
researchers develop an apparatus for their study. But instead
of using the apparatus for a controlled study, the apparatus is
embedded into an app, which is
then published on a mobile application market. Publishing the
app can attract a large number
of users and thus a large number of participants for the study.
Early examples used app stores
to collect user feedback on novel
interface artifacts via the reviewing system of Apple’s iOS Store.
However, the reviews were often
rather short and lacking in depth.
Thus, McMillan et al. explored
approaches to collect rich feed-
