To what extent are the representative NDC classification numbers for subject headings in NDLSH and NDC numbers assigned to bibliographic records matched?

Purpose: NDLSH are lists of subject headings, some of which have their corresponding classification numbers in NDC 9th ed., and are called "representative classification numbers." This paper investigates the extent to which the representative numbers in NDLSH match the classification numbers assigned to bibliographic records. It reports the detailed results on their matching, while referring to a preceding research on the same topic. Methods: Pairs of NDC numbers and NDLSH subject headings were extracted from bibliographic records created between 1997 and 2014. General topical subject headings and geographic ones were examined separately. The representative classification numbers for individual subject headings were obtained from Web NDL Authorities. Results: 1) For general topical headings, less than 20% of them have representative NDC numbers, most of which do not have sub-headings. More than 80% of subject headings with representative NDC numbers have records with NDC numbers matching the representative ones, while more than 10% of the NDLSH-NDC combinations that occurred in records were in agreement with those shown in NDLSH. Left-hand match on classification numbers increased the number of matching cases. Limiting the NDLSH-NDC pairs to those that occurred first in each record brought a substantial increase in the number of matching cases. 2) Only 6% of geographic subject headings have representative NDC numbers. More than 50% of such headings have records with NDC numbers that match the representative ones, while 15% of the NDLSH-NDC combinations occurred in records that agreed with those shown in NDLSH.