generic.knockbackResistance is percentage chance to ignore knockback, rather than being scaled

With the example bellow, the player who is holding/wearing the helmet rarely gets knocked, while most of the time he/she receives no knockback at all. This is of course not the intended result, as the player should be knocked back 50% as much as normal.

give @p 314 1 0 {AttributeModifiers:[

{AttributeName:"generic.knockbackResistance",Name:"generic.knockbackResistance",Amount:0.5,Operation:0,UUIDLeast:894654,UUIDMost:2872}

]}