@inproceedings{questiondifficultyestimationincommunity,
  title = {Question Difficulty Estimation in Community Question Answering Services},
  author = {Jing Liu and Quan Wang and Chin-Yew Lin and Hsiao-Wuen Hon},
  year = {2013},
  booktitle = {EMNLP 2013 10},
  url = {https://aclanthology.org/D13-1009},
}