It seems to me that, science apart, one can make a reasonable personal assessment of whether praying for material things (as per the OP) is significantly effective,
I would be interested in knowing who is doing the praying. A person who only wants to use God "might" not get the results that someone obeying God would get.
And often the results are not what I might wish for, but what I discover of how to stay in peace with God and how to love and care for others, instead of only trying to use people to solve my troubles. So, there can be this correction which is the answer I get

So, if your scientific studies did not reveal this . . . I'm curious who set up the study and who they chose to use as subjects.
How do you measure who is truly obeying God? "Have fun." I don't thing there is a scientific way to measure this. But unselfish motives can help. And then an unselfish person, I believe, is not going to be only or mainly about getting miracles of convenience.
People ask god for stuff whole cloth all the time. They do it and christians like yourself never jump in to say "god isn't a magical wish granter...don't you understand prayer?"
That's the canned response you save for atheists who point out the hypocrisy of the whole matter.
If I don't know someone personally, I am not likely to tell the person if their prayer request is for real or not. Also, in certain forums, we are not allowed to accuse or criticize people

So, even if we rightly can tell someone is praying out of selfishness of not being truly given to God, but only trying to use Him . . . we're not allowed by the rules, here, to directly accuse or criticize the person . . . if I understand the forum rules correctly.
But I can benefit from your comment, by remembering not to try to only use God for things I want
So - -

- - - there "might" be more to this, than some quick-fix conclusion. I think it is good to get to know someone personally, and spend time with the person, in order to really be able to help someone.
I have been one to first just criticize; now I find it is better and real in love to confront what is really wrong, but with hope for the person and investing myself as ready to stay with and help the person, or help to correct the person so the person becomes loving and caring about others as much as oneself.
I have a friend who can criticize herself, and stay busy with this. I offered how we need to pray and get real correction, not only criticize our own selves. And if there is something we messed up for ourselves, now we can care about others and not stay stuck in getting down on ourselves.
Our selfish stuff can get us our messes, but now we can do some caring for others. And prayer is for helping me to get real with God so I am caring about any and all people and not only about my own self and things. And this helps me to get stronger so my own things can't have power over me; and with this a lot of problems just get lost with the dumb things they might have taken out of my way
