I am not sure whether this prayer study was done to just to test God or done without love and faith for God, but with presumption by people who did not really believe or love God.
Better results maybe observed with people who have had some experience praying for others since many years and already have had results.
It depends who is praying, how he/she prays, the qualification or preparation of the minister before the prayer on the patient, the faith/love, the intensity, the motives, the intention, etc., the minister has within himself/herself.
Also, the patient’s sinful condition, guilt, fear, resentment, unforgiveness, bitterness, spiritual bondage etc. Thorough preparation of the patient’s heart and mind using scripture, confession, spiritual counseling, reassurance etc., His or her full agreement in acceptance of prayer, their love for God and expectant faith to receive the benefits of prayer by an anointed prayerful person. Sometimes, only a single session is needed and sometimes many such sessions or much longer.
Many such things as above may have to be noted by an experienced minister or ministers with some spiritual discernment. There may also have to be some constant and continuous intercessory prayers (with abstinence/fasting) by their relatives, friends, church members, etc., more the better. Otherwise, you will rarely see any good results or will see only disappointingly negative results. This is all sometimes needed because dark spiritual powers would want unbelieving people to experience firsthand the power of God and will try to oppose as much as possible.:
There should be some optimistic spiritual openness and strong faith at least on one side (either with the patient or the minister) to get some result. If both sides are fully open spiritually, divine intervention is bond to take place and one may see even physical healing, cure and miracles.
Even when there is no healing here or instead just hastening of death, you will see overflowing grace. The patient may be filled with love, joy and peace, and accepting of his/her condition and even ready to pass away happy without regrets!