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When variables are manually analyzed, and it is difficult to improve the accuracy beyond a certain level.

The combination of using both machine learning and a "manual" keyword approach is to increase accuracy and ensure that the generated statements could accurately describe any incident. [1] To some extent, the keyword analysis was also used as a buffer to compensate for misclassification by the machine learning algorithm.

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[1] Daniel Kurian, Fereshteh Sattari,  Lianne Lefsrud, Yongsheng Ma, Using machine learning and keyword analysis to analyze incidents and reduce risk in oil sands operations, Safety Science, 130(2020), 104873.