Degrees of freedom [General Sta­tis­tics]

posted by Mikkabel – Belgium, 2021-03-04 17:20 (43 d 12:16 ago) – Posting: # 22242
Views: 458

Hello everyone,

Recently, we performed a 4-treatment (T1, T2, T3 and T4), 4-period, cross-over study pharmacokinetic study.

Once the statistical analysis performed, I observed that for the comparison between T1 and T3 and between T2 and T4, the number of degrees of freedom for the fixed effect "period" is 2 instead of 3 (which is the case for the other comparisons). Furthermore, "Not estimable" is mentioned in the output of Winonlin.

For information, the statistical analysis was performed using ANOVA model (or equivalent parametric method) with fixed effects usually sequence, subject within sequence, period and formulation.

To be honest, I don't know how to fix it and I don't know how to interpret this.
Could you please inform me if it is an issue related to the software (Winonlin) or is it related to the model used?
Additionally, could you explain me how to interpret these results and what should be the impact on the results obtained form the analysis?

Thanks for your help

Complete thread:

 Admin contact
21,419 posts in 4,475 threads, 1,508 registered users;
online 10 (0 registered, 10 guests [including 4 identified bots]).
Forum time: Saturday 06:37 CEST (Europe/Vienna)

I never did anything worth doing by accident,
nor did any of my inventions come by accident;
they came by work.    Thomas Alva Edison

The Bioequivalence and Bioavailability Forum is hosted by
BEBAC Ing. Helmut Schütz