What percentage of patients born in 'Pembroke MA US' have 'allergy to grass pollen'?
percentage = MULTIPLY(DIVIDE(SUM(patient WHERE allergies.DESCRIPTION = 'Allergy to grass pollen'), COUNT(patient) WHERE birthplace = 'Pembroke MA US'), 100.0); born in Pembroke MA US refers to birthplace = 'Pembroke MA US'; allergy to grass pollen refers to allergies.DESCRIPTION = 'Allergy to grass';
SELECT CAST(SUM(CASE WHEN T2.DESCRIPTION = 'Allergy to grass pollen' THEN 1 ELSE 0 END) AS REL) * 100 / COUNT(T1.patient) FROM patients AS T1 INNER JOIN allergies AS T2 ON T1.patient = T2.PATIENT WHERE T1.birthplace = 'Pembroke MA US'