A scientific advisory panel has recommended that federal officials give top priority to comparing the effectiveness of competing medical strategies in areas that include treating prostate cancer, reducing hospital infections, and lowering the rate of unwanted pregnancies. In the report, a panel assembled by the Institute of Medicine released a list of 100 health topics that it said should get high priority as the Obama administration proceeded with a plan to spend $1.1 billion in comparing the effectiveness of competing drugs, medical devices, operations, and other treatments for specific health conditions.