I have not argued that a scientific study can only be valid if it controls everything. Look at my post #54. Rather it needs to control factors which are relevant for the effect being studied.
As the Masters paper I cited above argues, it may be more beneficial to study the effects of prayer on the wellbeing of the person who prays. That thinks of prayer more as a more physiological, social, or neurological activity like sleeping and meditating. It also limits the effects of prayer to something internal to one person.
Right, but all of these effects of zinc are on the person taking it. In the case of IP studies, we’re typically studying the effect of prayer on some other person that is being prayed for, who could be far away from the intercessor. There’s no known physical mechanism that can cause this. In that sense it has no better theoretical foundation than ESP or psychic powers. We also have the “confounding factor” of God, who is typically believed to be an important part of the causal chain that would make prayer efficacious. But scientists can’t control for God’s behavior.
Absolutely. And I would agree that any religious person who claims a simple linear relationship between praying for healing and getting healed is most likely wrong.