Whenever such studies or analyses come up in the media, I find that people are often eager to jump to causative conclusions on the lines of "oh females must have a natural inclination towards 'softer' fields" or (as in case of this article) "In wealthy nations, they believe that they have the freedom to pursue those alternatives and not worry so much that they pay less." However, even if we ignore the obvious correlation vs causation fallacy at play here, these conclusions conveniently ignore a million other societal factors that affect such decisions. For instance, as much of a gender-equality-utopia Scandinavian countries are, they're certainly not free of gender roles and the societal institutions that enforce those. While of course anecdotal, several of my friends from these countries have talked about how they faced invisible, passive-aggressive forms of bullying from fellow students (a large majority of them reportedly female) for having 'geeky' interests such as math. When presented with other options that may eventually be equally or slightly less fulfilling, but come without the social pressure, it makes sense to most people to go with the flow. So much for "natural inclinations"...