In cross-sectional analyses , there was a strong relationship between the 2 SAQ angina frequency questions ( ie , frequency of angina and SL NTG use ) and the corresponding diary responses , with correlation coefficients of -0.64 for angina frequency ( 95 % confidence interval,-0 .68 to -0.60 ) and -0.69 for SL NTG use ( 95 % confidence interval , -0.73 to -0.66 ) .