quote So we have an observable phenomenon (human belief in the existence of the supernatural) that requires scientific explanation. The question posed in this thread is therefore: How do we scientifically investigate the cause of this observable phenomenon? unquote
This is quite tangled, in at least two ways.
First, you cannot investigate a belief - by the nature of belief. A belief is the decision to act on one of two or more necessarily unproved or unprovable propositions. Not only that, but the decision to act on any one of the propositions is always i) beyond logical reproach even if it is pragmatically a matter of reproach ii) unrelated to the facts on which the unproved propositions are based.
The other tangle was the unannounced slide from investigating the putatively private or psychological nature of belief (even though the propositions that make up a belief are always public, never private), to the idea that investigating a belief was investigating the propositions or facts behind the propositions of a belief. So you can understand if I ask you what you think you want to investigate?
Edited by John Jones, : No reason given.