# Bioequivalence and Bioavailability Forum

Back to the forum  2018-06-22 02:22 CEST (UTC+2h)
sudy
Junior

India,
2017-08-01 13:29
(edited by sudy on 2017-08-01 13:49)

Posting: # 17641
Views: 1,640

## Inter subject CV calculation [General Sta­tis­tics]

Hi all,
Can anyone suggest any logic on below results?

Why Inter subject CV is not calculated for Cmax?
Is this formula is correct to calculate between subject variability on log transformed data for two way cross over study?
If i calculate manually in excel, I am getting the value around 28% for cmax. But SAS gives error.
One more point i have noted that, the MSS is very low by SAS, but manually this value is very high.
Why R-square is very low for Cmax?

Helmut
Hero

Vienna, Austria,
2017-08-01 14:33

@ sudy
Posting: # 17642
Views: 1,401

## √x, where x<0

Hi sudy,

next time you upload a PNG please 640px (longest side) or better only the numbers. I had a hard time to read the results.

» Why Inter subject CV is not calculated for Cmax?

Unless you want to deal with imaginary numbers, the square root of a negative value is not defined. Since ℯ(MSs – MSe)/2 = 0.994155, √–0.005845 don’t work.

» Is this formula is correct to calculate between subject variability on log transformed data for two way cross over study?

Yes. See there.

» If i calculate manually in excel, I am getting the value around 28% for cmax. But SAS gives error.

Please check what you have done in Excel. Cannot work:

```A1 0.06596695 B1 0.07769188 C1 =(A1-B1)/2 D1 =EXP(C1) E1 =D1-1 F1 =100*SQRT(E1)```

What do you get? 28% is CVintra – in Excel-lingo `100*SQRT((EXP(B1)-1))`.

» One more point i have noted that, the MSS is very low by SAS, but manually this value is very high.

No idea. I don’t have a crystal ball which could tell me what you are doing “manually”.

» Why R-square is very low for Cmax?

Higher variability than the ones of AUCs ⇒ lower R2. As expected.

Cheers,
Helmut Schütz

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