Don't think anybody has the ability to conduct an objective study,
other than the three credit bureaus that keep that data as
proprietary.

The banks themselves don't do independent analyses of this, they take
the credit score itself, plus your income, asset and debt levels, to
decide on credit.

The credit bureaus say that they look at how much you owe vs. total
credit available- in other words, are your credit cards maxed out, or
do you use them only a little.

So it seems that if you have ten credit cards each with a $5000 limit
and you owe $5000, cancelling one won't make that much (or maybe any)
difference (owing 10% vs. 11%). But if you have only 3 of them and
cancel one, then you've gone from 33% to 50% and that's a big change.

Note that usage includes what's outstanding when they measure it- so
if you use your cards a lot but pay them off every month you will
still show some 'debt.'