The effect of study design and analysis methods on recovery rates in Bell's palsy


  • This work was funded by Uppsala University; GlaxoSmithKline, Sweden; Pfizer AB, Sweden; Acta Otolaryngologica Foundation; Rosa and Emanuel Nachmansson's Foundation; Stig and Ragna Gorthon Foundation; Torsten Birger Segerfalk Foundation; Margit Arstrup's Foundation; the County Council of Skåne; and Helsinki University Central Hospital Research Funds. Mats Engström, MD was paid by GlaxoSmithKline for a lecture on Bell's palsy in 2001. The other authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.



We investigated how study design affects the rate of recovery in Bell's palsy.

Study Design:

Prospective, randomized, double-blind, placebo-controlled, multicenter trial.


Data were extracted from the Scandinavian Bell's palsy study, which included 829 patients. The study design was factorial; 416 patients given prednisolone, 413 not given prednisolone, 413 patients given valacyclovir, 416 not given valacyclovir. Data were analyzed with intention-to-treat principle and complete-case analysis methods and recovery was defined as Sunnybrook score 100, House-Brackmann grade I or ≤grade II at 12 months.


With the intention-to-treat principle and last-observation-carried-forward method (n = 829) and recovery defined as Sunnybrook 100, 300 of the 416 patients (72%) receiving prednisolone had recovered compared with 237 of the 413 (57%) who did not receive prednisolone (P < .0001). With recovery defined as House-Brackmann grade I, the corresponding recovery rates were 324 of 416 (78%) and 266 of 413 (64%) (P < .0001). With complete-case analysis and recovery defined House-Brackmann grade I (n = 782), 335 of 389 patients (86%) given prednisolone recovered compared with 277 of 393 (70%) in the group not given prednisolone (P < .0001). With recovery defined as House-Brackmann ≤grade II (n = 797), the corresponding recovery rates were 380 of 396 (96%) and 353 of 401 (88%) (P < .0001). The analysis method affected the recovery rates in the valacyclovir and no-valacyclovir groups in a similar way as in the prednisolone and no-prednisolone groups.


Recovery rates in a Bell's palsy study are substantially affected by the choice of analysis method and definition of recovery. Laryngoscope, 2009