2.Please clearly understand the f/f ( there is one question on choice) No association between exposure and disease : AR=0, RR=1, OR=1 -Positive association between exposure and disease (more exposure, more disease) AR>0, RR>1 OR>1 , -Negative association between exposure and disease (more exposure, less disease), RR <1(fraction) , AR<0 (negative), Negative association between exposure and disease , the attributable factor is protective factor