  Artificial Intelligence (AI) software systems, such as Sentiment Analysis
(SA) systems, typically learn from large amounts of data that may reflect human
biases. Consequently, the machine learning model in such software systems may
exhibit unintended demographic bias based on specific characteristics (e.g.,
gender, occupation, country-of-origin, etc.). Such biases manifest in an SA
system when it predicts a different sentiment for similar texts that differ
only in the characteristic of individuals described. Existing studies on
revealing bias in SA systems rely on the production of sentences from a small
set of short, predefined templates.
  To address this limitation, we present BisaFinder, an approach to discover
biased predictions in SA systems via metamorphic testing. A key feature of
BisaFinder is the automatic curation of suitable templates based on the pieces
of text from a large corpus, using various Natural Language Processing (NLP)
techniques to identify words that describe demographic characteristics. Next,
BisaFinder instantiates new text from these templates by filling in
placeholders with words associated with a class of a characteristic (e.g.,
gender-specific words such as female names, "she", "her"). These texts are used
to tease out bias in an SA system. BisaFinder identifies a bias-uncovering test
case when it detects that the SA system exhibits demographic bias for a pair of
texts, i.e., it predicts a different sentiment for texts that differ only in
words associated with a different class (e.g., male vs. female) of a target
characteristic (e.g., gender). Our empirical evaluation showed that BisaFinder
can effectively create a large number of realistic and diverse test cases that
uncover various biases in an SA system with a high true positive rate of up to
95.8\%.
