Too vague!

Since 1990, US population has increased 30% while the (inflation corrected) GDP has increased 90%. So something improved. I'm going to (arbitrarily) say it was computer literacy, since home PC ownership went from 15% of households to 85% of households in that time period.

What can you counter with to say that the improvements were from market efficiency? If we never had HFT, how much lower would the GDP be?