To many ailments, mental or physical and especially spiritually, prayer have been a go to "medicine" recommended to people of all stations.
When did the church start trying to evaluate the effectiveness of prayer? How would for example a theological discussion look like between two different bishops having different opinion on how the prayer should be done/how long prayer should be, etc.
And was any such discussion rooted in a lack of result for the patient? For example if prayer was prescribed against back pain, would there be some systematic evaluation if prayer seemed useless at aleveating the ailement?
The search for evaluating prayer and also the search "to perfect prayer" also applies to Battle prayers and all sorts of prayers.
I would imagine a king would want the best prayer/blessing before battle for example.
This is probably not the era you're asking about but there have been several attempts to prove that prayer is effective in the evidence-based medicine era. Publication bias (probably) skews the literature towards the positive.
Two randomised controlled trials tested the effect of remote intercessory prayer (praying for persons unknown) on outcomes in patients admitted to an intensive coronary care unit.1 2 Both studies showed a beneficial effect. A recent systematic review of the efficacy of distant healing concluded that “approximately 57% (13 of 23) of the randomised, placebo-controlled trials of distant healing . . . showed a positive treatment effect” and that “the evidence thus far warrants further study.”3
The purpose of the present study was to extend these observations to patients with another severe disorder, bloodstream infection. As we cannot assume a priori that time is linear, as we perceive it,4 or that God is limited by a linear time, as we are,5 the intervention was carried out 4-10 years after the patients’ infection and hospitalisation. The hypothesis was that remote, retroactive intercessory prayer reduces mortality and shortens the length of stay in hospital and duration of fever.
The quoted study is Effects of remote, retroactive intercessory prayer on outcomes in patients with bloodstream infection: randomised controlled trial. That is, they randomised people who had recovered years earlier to "retroactive" prayer, and found a time-defying beneficial effect. The article is somewhat tongue-in-cheek and was done to show how easy it is to 'prove' impossible results.
This sort of formal evaluation of effects didn't really get going until after WWII, although there are a few attempts at comparing outcomes in a controlled way going back centuries earlier. The chances that a formal study, especially one controlling for placebo effects, took place more than a few decades ago is unlikely.