Hand tapping in these patients declines linearly at a rate of 5.1 taps per year ( p < 0.0001 ; 95 % CI = 3.8 to 6.3 taps ) , and for each additional year of age patients could perform 0.9 fewer taps ( main effect of age : p = 0.0007 ; 95 % CI = 0.4 to 1.4 ) .