Factor OR, P value Comparison group
NFB type (batteries and magnets) OR= 6.5, P=0.01 All other NFB together
More than one removal attempt OR= 6.4, P=0.01 Removal in the first attempt
Posterior insertion of NFB OR= 2.4, P=0.02 Anterior insertion
Left-side insertion of NFB OR= 1.8, P=0.02 Right-side insertion