There are two useful questions to ask when trying to define a need for information:

1. Why is the information needed?

One way of defining a need for information may be the purpose for which you need it (e.g. you need it to make a particular decision, you need it for some academic work you are doing, you need it for your own personal interest).

Mary needs information specifically for her module project. The brief for her project will help to set the context and define both the level and the amount of information needed.

2. What do you know already?

Considering what you already know can be a useful starting point – it will enable you to identify the gaps. It can be helpful to make some notes about your knowledge of the subject.