The need of a carefully defined review question, generally with a focus on efficacy, has been frequently emphasized. The first systematic review book in the BMJ went much farther, stating that systematic reviews are hypothesis-testing procedures. This is certainly an accurate statement for meta-analyses but not for all types of systematic reviews. For example, exploratory reviews do not necessarily seek to answer a specific question and therefore do not have hypotheses to test. An "exploratory" review is one that seeks to describe the range of evidence available on a topic, rather than try to summarize it or predict what might happen if studies were conducted now. As its name suggests, an exploratory review is done to explore the extent of research activity on a topic, to detect gaps in knowledge and opportunities for further investigation. It may also be useful when there is no clear question to be answered by a systematic review but information needs to be collected for other reasons (for example, to provide baseline data for future comparisons). A focused review aims to solve a specific problem or achieve a specific goal. The quality and relevance of the evidence obtained from the focused reviews will influence the usefulness of the results for decision making.