Fig. 2

a and b One-way sensitivity analyses (tornado diagrams) for the comparisons of Booklet vs. NC (a) and Combined vs. NC (b). Horizontals bar indicate the change in every cost variable ranging from percentiles 5 to 95 %. The graph shows the influence of the change in one unit cost in the ICER (€ per sickness absence day), when other values remain at their base level. Around the ICER, bars may be asymmetric because of the Bayesian statistical procedure. In both graphs, variables were sorted according to their influence in the comparison of Booklet vs. NC (most influential variable on top). Variables OH-else, HOSP-Nurse, PRIV-Nurse, HOSP-Phys, HOSP-else and INTCOST have been deleted because of minimal effects in the ICER. The descriptions of all cost-items are shown in the Additional file 1 [Booklet, Back Book booklet group; Combined, Back Book with oral advice group; NC, natural course of LBP group]