# [R] miscalculate AUC

leeznar at yahoo.com.tw leeznar at yahoo.com.tw
Tue Oct 30 10:25:34 CET 2007

```Dear R-helper,

I have subject 1, 2, 3 and formulation S, MF, MM.  I
have a problem in calculating AUC.  The AUC (0~t) in
formulation MF and MM were miscalculated, but I don’t
know where my problem is.  Here is my code and output.

test<-function( InVVTestindex,
separateWindows=TRUE)
{
for( i in 1:length(unique
(InVVTestindex\$subject))){
x<-InVVTestindex\$time[InVVTestindex\$subject==i]

y<-InVVTestindex\$concentration[InVVTestindex\$subject==i]

v<-InVVTestindex\$formulation[InVVTestindex\$subject==i]
w<-InVVTestindex\$pH[InVVTestindex\$subject==i]
#calculate AUC
auc<-0
for(i in 2:length(time)) {

auc[i]<-1/2*(time[i]-time[i-1])*(concentration[i]+concentration[i-1])
auc[i]<-auc[i]+auc[i-1]
}
return(list(auc=auc))
}
#Output
cat("<< Output >>\n")
output<-data.frame(w,i,v,x,y,AUC)

colnames(output)<-list("pH","subject","formulation","time","concentration","AUC(0~t)")
show(output)
cat("\n\n")
}
}

<< Output >>
pH subject formulation time concentration
AUC(0~t)
1  6.8       1           S  0.0          0.00
0.0000
2  6.8       1           S  0.5        110.26
27.5650
3  6.8       1           S  1.0        116.17
84.1725
4  6.8       1           S  1.5        130.20
145.7650
5  6.8       1           S  2.0        145.77
214.7575
6  6.8       1           S  3.0        123.75
349.5175
7  6.8       1           S  4.0        123.05
472.9175
8  6.8       1           S  5.0         82.35
575.6175
9  6.8       1           S  6.0         48.62
641.1025
10 6.8       1           S  8.0         26.51
716.2325
11 6.8       1           S 10.0          3.04
745.7825
12 6.8       1           S 12.0          2.87
751.6925
13 6.8       1           S 24.0          2.74
785.3525
14 6.8       1          MF  0.0         0.00  752.4725
15 6.8       1          MF  0.5         91.67
775.3900
16 6.8       1          MF  1.0        216.78
852.5025
17 6.8       1          MF  1.5        179.91
951.6750
18 6.8       1          MF  2.0        187.02
1043.4075
19 6.8       1          MF  3.0        176.15
1224.9925
20 6.8       1          MF  4.0        171.24
1398.6875
21 6.8       1          MF  5.0        157.83
1563.2225
22 6.8       1          MF  6.0        149.15
1716.7125
23 6.8       1          MF  8.0        142.18
2008.0425
24 6.8       1          MF 10.0        107.56
2257.7825
25 6.8       1          MF 12.0         86.37
2451.7125
26 6.8       1          MF 24.0          9.30
3025.7325
27 6.8       1          MM  0.0          0.00
2914.1325
28 6.8       1          MM  0.5        114.18
2942.6775
29 6.8       1          MM  1.0        160.72
3011.4025
30 6.8       1          MM  1.5        152.28
3089.6525
31 6.8       1          MM  2.0        125.05
3158.9850
32 6.8       1          MM  3.0        118.97
3280.9950
33 6.8       1          MM  4.0        123.26
3402.1100
34 6.8       1          MM  5.0        143.46
3535.4700
35 6.8       1          MM  6.0        137.00
3675.7000
36 6.8       1          MM  8.0         91.48
3904.1800
37 6.8       1          MM 10.0         52.46
4048.1200
38 6.8       1          MM 12.0         15.39
4115.9700
39 6.8       1          MM 24.0          8.00
4256.3100

Best regards,
Hsin-Ya Lee

```