Formulating your question:

GOOD!

This is a much better group of key concepts. It clearly outlines the:

• patient problem: sickle cell disease
• intervention: prophylactic penicillin
• comparison: no prophylactic penicillin
  
• outcome: prevention of infections

While you may not need all of these concepts in your search strategy, they help you clearly focus your question so that you will be able to identify the best articles to answer your question. When considering good evidence for the effectiveness of therapies, one should look for clinical trials or randomized clinical trials. We will consider this type of study as we conduct our search.

The formulated question might be:

In children with sickle cell disease, is long term use of prophylactic penicillin absolutely necessary to prevent infections?