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:

• Language
• Topic
• Digital Object type
• Archive Type

In order to avoid confusion, date-related filters are not available at the moment, but we are looking into extending the options available to our Content Providers to automatically create machine-readable dates during data processing. You can still sort your document searches by date.

See our Research Tools section for more details.