  Background: Assisting moderators to triage harmful posts in Internet Support
Groups is relevant to ensure its safe use. Automated text classification
methods analysing the language expressed in posts of online forums is a
promising solution. Methods: Natural Language Processing and Machine Learning
technologies were used to build a triage post classifier using a dataset from
Reachout mental health forum for young people. Results: When comparing with the
state-of-the-art, a solution mainly based on features from lexical resources,
received the best classification performance for the crisis posts (52%), which
is the most severe class. Six salient linguistic characteristics were found
when analysing the crisis post; 1) posts expressing hopelessness, 2) short
posts expressing concise negative emotional responses, 3) long posts expressing
variations of emotions, 4) posts expressing dissatisfaction with available
health services, 5) posts utilising storytelling, and 6) posts expressing users
seeking advice from peers during a crisis. Conclusion: It is possible to build
a competitive triage classifier using features derived only from the textual
content of the post. Further research needs to be done in order to translate
our quantitative and qualitative findings into features, as it may improve
overall performance.
