What is the difference between trade_volume and trade_volume_normalised?

Trading volumes can be easily faked by rogue exchanges and to combat fake exchange volume data, CoinGecko introduced normalised volume whereby web traffic statistics are taken into account when considering the trading volume. 

In short, trade_volume is trading volume reported by exchanges while trade_volume_normalised is provided by CoinGecko to reflect a closer truth to the actual volume traded on the exchanges. 

To understand further, you may read this article on Trust Scores. 

Note: We do not provide normalised volume for historical exchange data at the moment (volume_chart endpoint).