they say you have to build up an entire ecosystem of life in your soil to attract the most worms.

I'm trying to find more ways of attracting them but it's hard to get specific studies that show things in a quantifiable way from the gardening community. Some say leaves on the surface attract worms, some say it's composted things, some say it's compost that hasn't completely been broken down yet. But, I have yet to see studies that show precisely the percentage of worms increased by various types of organic matter. What's the optimal approach? other than just adding more organic matter.

i'm adding as much organic matter on top as I can from a variety of sources. but, it'd be great to get some actual specifics on what's most effective.