According to random50 on the galciv2 forums:
1. Bonuses (and presumably penalties, if your chosen one is not in office) from the ruling party are applied as racial bonuses. They are included in the figure on the "civilization stats" screen.
2. Bonuses obtained from the tech tree (eg +10 for Xeno Economics) are applied as racial bonuses. They are included in the figure on the "civilization stats" screen.
3. The government forms are wrongly reported. They ONLY give an economy bonus. The real rate is lower than reported as well. They give 10% bonus each and are applied as racial bonuses. This is NOT included in the figure on the civilization stats screen.
4. When the amount of money in treasury exceeds 20,000 BC, the race receives a malus of 20% to its econ ability. If you're running just a few hundreds BC surplus, better spend all the money over 20,000, or you'll get the next turn negative income.
- Economy
The income on a planet is given by
34.5 * sqrt(population_in_billions) * tax_rate * (1 + (sum from buildings on planet)) * (1 + (sum from racial bonuses/maluses) )
I'm not certain about the 34.5, but it's at least very close to that number (34.x). So for example, if you have a Star Democracy, a 20% inherent economy bonus, a 10% bonus from the ruling political party and a tax rate of 50% then you will have
1) A multiplier of 0.5 as tax rate.
2) The treasury is above 20,000 BC, so malus 20% applies.
3) A racial bonus multiplier of 1 + 0.2(inherent) + 0.1(political party) + 0.15(bonus for researching economics through to stock exchanges) + 0.2(from Star Democracy) - 0.2 for treasury above 20TC = 1.45
4) A planet with 3 stock exchanges and an economic capital would have a buildings multiplier for the planet of 1 + (3 * 0.3 (stock exchanges) + 0.5 (econ capital)) = 2.4
So that planet would provide you with
34.5 * sqrt(pop) * 0.5 * 1.45 * 2.4 BC income every turn.
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Anyone want to format this nicely for the article?