Take s&p 500 for example.
When I look at the index (US 500) in IG in Feb 24 - 2022 I see it had volume 2,841,240. The day after, Fri 25th Feb 2022, I see volume 1,869,036.
If I look in yahoo finance, at symbol ^GSPC, the volume is completely different, both as an absolute value as well as relative.
^GSPC reports 6,752,130,000 for 24 Feb, and 5,177,060,000 for 25 Feb.
The absolute values are completely different at a glance, but even the relative change between one day and the other is inconsistent across both volumes. So based on IG volumes, the amount traded in 24 Feb is roughly 1.30x the amount traded on the 25th. Now on GSPC, it's roughly 1.52x. Thats more than 20% discrepancy between whats reporting as volume decrease from one day to the next in both data sources.
So my questions are:
* which of the 2 sites has the accurate volume?
* why is there such discrepancy?