Database schema:

CREATE TABLE "Answer" (
	"AnswerText" TEXT -- example: ['44', '37'],
	"SurveyID" INTEGER -- example: ['2014', '2016'],
	"UserID" INTEGER -- example: ['2', '1'],
	"QuestionID" INTEGER -- example: ['2', '1'],
	PRIMARY KEY ("UserID", "QuestionID"), 
	CONSTRAINT fk_answer_question FOREIGN KEY("QuestionID") REFERENCES "Question" (questionid),
	CONSTRAINT fk_answer_survey FOREIGN KEY("SurveyID") REFERENCES "Survey" ("SurveyID")
)


CREATE TABLE "Question" (
	questiontext TEXT -- example: ['What is your age?', 'What is your gender?'],
	questionid INTEGER -- example: ['2', '1'],
	PRIMARY KEY (questionid)
)


CREATE TABLE "Survey" (
	"SurveyID" INTEGER -- example: ['2014', '2016'],
	"Description" TEXT -- example: ['mental health survey for 2014', 'mental health survey for 2016'],
	PRIMARY KEY ("SurveyID")
)

Question: What was the percentage for the answer of "Yes" was given to the question "Has your employer ever formally discussed mental health (for example, as part of a wellness campaign or other official communication)?"?
Evidence: percentage = divide(count(QuestionID = 15& AnswerText = 'Yes'), count(QuestionID = 15))*100%

SQL:
SELECT CAST(SUM(CASE  WHEN T1.AnswerText LIKE 'Yes' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.UserID) FROM Answer AS T1 INNER JOIN Question AS T2 ON T1.QuestionID = T2.questionid WHERE T2.questiontext LIKE 'Has your employer ever formally discussed mental health (for example, as part of a wellness campaign or other official communication)?'