A factor in the workers' compensation premium development is the experience modification factor - or the "Experience Mod," & "X-Mod" or just plain "Mod."
In general terms, the insured's individually developed Experience Mod can have no effect, a positive effect or a negative effect on the insured's workers' compensation premium. From a broad perspective, the experience mod in some ways "customize" the premium for that insured. (Of course, underwriters can negate the effects of the experience mod with debits or credits, but this is a wholly different conversation.)