The gap between Welsh GVA (gross value added) and that of the UK was evident before we had the National Assembly and devolution. Since then, while our devolved Assembly has had few powers and tools to impact prosperity levels, GVA has further declined compared to the UK. In 1999, the first year of devolved government, it was 72% compared to the UK. There have been a handful of years since then where Welsh GVA has nudged above the UK level, but in the latest ONS figures, it is at 71.4%.
Article source: http://www.huffingtonpost.co.uk/leanne-wood/welsh-valleys-brexit_b_11777630.html?utm_hp_ref=uk-politics&ir=UK+Politics