  To provide click simulation or relevance estimation based on users' implicit
interaction feedback, click models have been much studied during recent years.
Most click models focus on user behaviors towards a single list. However, with
the development of user interface (UI) design, the layout of displayed items on
a result page tends to be multi-block (i.e., multi-list) style instead of a
single list, which requires different assumptions to model user behaviors more
accurately. There exist click models for multi-block pages in desktop contexts,
but they cannot be directly applied to mobile scenarios due to different
interaction manners, result types and especially multi-block presentation
styles. In particular, multi-block mobile pages can normally be decomposed into
interleavings of basic vertical blocks and horizontal blocks, thus resulting in
typically F-shape forms. To mitigate gaps between desktop and mobile contexts
for multi-block pages, we conduct a user eye-tracking study, and identify
users' sequential browsing, block skip and comparison patterns on F-shape
pages. These findings lead to the design of a novel F-shape Click Model (FSCM),
which serves as a general solution to multi-block mobile pages. Firstly, we
construct a directed acyclic graph (DAG) for each page, where each item is
regarded as a vertex and each edge indicates the user's possible examination
flow. Secondly, we propose DAG-structured GRUs and a comparison module to model
users' sequential (sequential browsing, block skip) and non-sequential
(comparison) behaviors respectively. Finally, we combine GRU states and
comparison patterns to perform user click predictions. Experiments on a
large-scale real-world dataset validate the effectiveness of FSCM on user
behavior predictions compared with baseline models.
