There have been scientific studies that conclude prayer has little or no affect?
First let me just say that just because were Christians, God owes us nothing. Let me tell you what prayer does Scientist boy. When I pray to God I'm simply acknowledging that he is God, that he is control and that he is sovereign. I'm showing respect for his greatness, it's a sign of worship. I'm admitting my dependence on him. I'm showing that I am thankful and grateful for all he has done.
Besides I'm commanded to do so. (1st Thess. 5:17). I don't look at God as a Genie in a bottle to grant my every wish. And I don't know how we can say prayer doesn't work because people who have faith don't get any more "healed" then skeptics? I pray for skeptics just about every day. Who knows that the "sick" Atheist in a hospital bed somewhere doesn't have a Christian Granma or friend praying for them?
The Bible does say that God doesn't necessarily answer prayers that are Insincere (Matt. 6:5) or selfish (James 4:3) or your because your to proud(Luke 18:10-14) or unbelief or you have unconfessed sin in your life.
When your having a bad day or week or whatever, instead of asking God to make things better, we should ask him to give us the wisdom and or strength to get through these trials?
Atheist friend, try this tonight before you go to bed, close your eyes and say "thanks God, Amen". See what happens, and during the next scientific study maybe they will include a poll and your answer to the question of whether God hears your prayers or not will surprise even you?