  Social media (SM) data provides a vast record of humanity's everyday
thoughts, feelings, and actions at a resolution previously unimaginable.
Because user behavior on SM is a reflection of events in the real world,
researchers have realized they can use SM in order to forecast, making
predictions about the future. The advantage of SM data is its relative ease of
acquisition, large quantity, and ability to capture socially relevant
information, which may be difficult to gather from other data sources.
Promising results exist across a wide variety of domains, but one will find
little consensus regarding best practices in either methodology or evaluation.
In this systematic review, we examine relevant literature over the past decade,
tabulate mixed results across a number of scientific disciplines, and identify
common pitfalls and best practices. We find that SM forecasting is limited by
data biases, noisy data, lack of generalizable results, a lack of
domain-specific theory, and underlying complexity in many prediction tasks. But
despite these shortcomings, recurring findings and promising results continue
to galvanize researchers and demand continued investigation. Based on the
existing literature, we identify research practices which lead to success,
citing specific examples in each case and making recommendations for best
practices. These recommendations will help researchers take advantage of the
exciting possibilities offered by SM platforms.
