As you can see from the above examination of what an index IS by how it is used, a GOOD index then is a reference that enables a reader to find something in a large or complex document EASILY.  Thus, the more wording combinations are covered, the more people will find your index (and therefore your document) easy to use.  When your index is so thorough that most readers will find what they are looking for on their first attempt, you will have rivaled computer search engines in the ease of finding reference material, and your index will be very valuable to the document it references, and therefore to its readers.

 

Indexes can also be combined to form one large index that can refer to multiple documents.  An example of this is for an encyclopedia.  Each volume has its own index that refers to articles in that volume.  And then there is often a single "Index" volume that contains one big index that covers the entire encyclopedia set.

 

Not only is it possible to create an index that fulfills the definition of a GOOD INDEX, but it is actually easy to do so.  Be prepared however:  creating a GOOD index takes a lot of work.  Fortunately, doing the amount of work required is both rewarding and produces an index you can be proud of.