What percentage of male patients who first presented to the hospital in 1981 were diagnosed with BEHCET?
male refers to SEX = 'M'; first presented to the hospital in 1981 refers to YEAR(`FIRST DATE`) = '1981'; BEHCET refers to diagnosis; calculation = DIVIDE(SUM(DIAGNOSIS = 'BEHCET') where YEAR(`FIRST DATE`) = '1981', MULTIPLY(COUNT(YEAR(`FIRST DATE`) = '1981')), 100)
SELECT CAST(SUM(CASE WHEN Diagnosis = 'BEHCET' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(ID) FROM Patient WHERE STRFTIME('%Y', `First Date`) = '1981' AND SEX = 'M'