En forklaring kan være, at da det meste af skattepolitikken er af national karakter med meget lille differentiering inden for det enkelte land, har der været begrænset mulighed for at analysere virkningen af forskellene mellem visse områder eller visse grupper af arbejdere.
One explanation may be that, since most fiscal policies operate on a national level, with little or no differentiation within that state, the scope for examining the effects of variations between localities or groups of worker has been limited.