When they don't release the data and/or methodolgy, you have to treat the result the same: garbage.
They could be completely making up data or demonstrating the gold standard example of pristine data collection and brilliant analysis but we'd never know.. and for some reason, they don't want to tell us.
> for some reason, they don't want to tell us
It should be pretty clear why they don't want to show and tell.
I'm quite confident on why they don't want to share their data and/or methodology but there could be legitimate reasons and I want to be open to those.
Regardless, without that information, we can only evaluate them based on how rigorus they've been in the past:
Are the researchers and organizations involved known for effective data collection and solid analysis?
>but there could be legitimate reasons and I want to be open to those
Then they the should just say what those reasons are. What's there to hide?
You can't expect to be opaque and then the public to blindly trust you simply on the basis that you call yourself experts.