Democracy has one definition no matter where you go. That is political adversary and the sharing of power between more than one party.
"Is it United States of America’s model of economy, or is it China or Japan?"
Communist China is not a Democracy. lol
"Feng’s results were to a certain extent less intriguing than expected. Even though his statistical results showed no relationship between democracy and economic growth, he stressed on the indirect rather than a direct relationship between the two variables."
The idea that the more a country becomes closer to Democracy is not a direct variable is wrong. A direct variable means a nexus without any connections or nexus. We can see the direct connection between countries that allow more expression of option for leadership to markets. This means there is a direct connection. For example, any country that has started to become more Democracy style in representation has seen a huge bust in markets. This is because for the leader to be represented he must be able to enrich their people. That is a Direct connection voting equates to market growth. As it means the people are able to vote for the people who are the best providers.