How many users answered "Yes" to the question "Have you had a mental health disorder in the past?" in 3 consecutive years starting from 2016?
question refers to questiontext; answered 'Yes' to question refers to AnswerText = 'Yes'; 3 consecutive years starting from 2016 refers to SurveyID = 2016 and SurveyID = 2017 and SurveyID = 2018
SELECT COUNT(T2.UserID) FROM Question AS T1 INNER JOIN Answer AS T2 ON T1.questionid = T2.QuestionID WHERE T2.SurveyID IN (2016, 2017, 2018) AND T1.questiontext LIKE 'Have you had a mental health disorder in the past?' AND T2.AnswerText = 'Yes'