565 Subfield $c - Unit of analysis:

Subfield $c contains the subject to which variables in case files or data bases refer; for example, convicts in correctional files, workers in personnel records, or casualities in emergency room intake files.

Example:

565 0#$3Automobile consumer survey files$a8;$baddress;$bmanufacturer of vehicle;$bmodel of vehicle;$bdate of purchase;$bdate of 1st major repairs$bcurrent mileage;$bdate of latest repair;$dcomplaint filers 1981 January 1 through 1983 December 31;$cnew vehicle registrants