Can we attribute how advanced many Scandinavian countries are to how successful they were at staying out of WW2? Could there be a correlation, and are there any studies that look at this?

Are you referring to Scandinavian / Nordic countries as a whole, or relative to each other?

Denmark - occupied by Nazi Germany Norway - occupied by Nazi Germany Sweden - neutral, sold arms and strategic materials to both the allies and Germany Iceland - allied nation, not directly threatened Finland - involved in separate war with USSR with some help from Germany as co-belligerent.

So in order to prove/disprove, you are looking at studies to compare Sweden vs Denmark and Norway...?