Filters are document aggregations assembled based on some shared characteristic by a collector, not by the creator. They are a powerful tool, but they can be misleading as some of them require extra tagging on part of the institutions that is not always done (this really depends on the tradition of the single institution in dealing with digital data).

Our advice is that the filters that are always safe to use (because they are assigned automatically) are:

• Country
• Archival Institution
• Levels
• Contains Digital Object

On the other hand, the filters that can be misleading and exclude relevant results that have not been tagged are:

• Date
• Language
• Topic
• Digital Object type
• Date-related filters
• Archive Type

See our Research Tools section for more details.