Can research really say something (anything) about the inner life of faith and doubt, trust and uncertainty that is religious belief?It is important to remember that doubt and uncertainty are not, strictly speaking, part of the life of faith. Faith is trust. Doubt and uncertainty are lack of trust.
Thus, we may speak of the waxing and waning of faith, but we cannot speak of doubt and uncertainty as being part of the faith life any more than we can speak of cholera and dysentery as being part of the healthy lifestyle.
You might say, "But doubt and uncertainty are a necessary part of faith! To deny that all faith includes doubt would be both untrue and, to me, a sign of hubris!" This isn't true, as is easily demonstrated. Simply take that phrase and substitute the appropriate terms: "To deny that all health involves dysentery is both untrue and a sign of hubris!" Does that make sense?
Too many people view the word "faith" as they do the word "cleave" - they treat "faith" as if it were its own antonym. It isn't. Doubt is not a necessary part of faith. To say that doubt happens to otherwise faithful people is identical to saying that dysentery happens to otherwise healthy people - a true statement, but a non sequitor.
Theology is a science. Faith, at least in Christian experience (and arguably in Judaic experience) is an evidence-based attitude. You could make arguments against this position in other traditions, of course. Hinduism is not faith-based, and Buddhism isn't even, properly speaking, a theology. But the whole purpose of the OT in Jewish tradition is to record evidence that God is trustworthy, the whole purpose of the NT is to record the evidence of what the trusted God has done.
If we were to look at experimental science, we would see the role of doubt as appropriate only to one's own interpretation of available data. I don't doubt the facts. I doubt - at most - that I personally have correctly collected, interpreted or presented the facts. The role of doubt for a theologian is the same - I don't doubt reality, I doubt my own ability to grasp it correctly. So, I can only struggle with faith in myself, I cannot, properly speaking, struggle with faith in God..
In short, I trust God, I don't trust me.
THAT is the only proper way to discuss doubt in regards to faith.