Double Indexing
  • Avoiding double indexing

Double (or redundant) indexing is the practice of indexing the same service concept using two or more service terms. Double indexing is not a recommended practice.

Note that double indexing involves service concepts rather than database service records. For example, an agency may offer a single program that encompasses multiple service concepts — such as a program that offers both sack lunches and emergency clothing to homeless persons. In this situation, it is reasonable to create a single database record that reflects both of those services and index them with the Taxonomy terms Sack Lunches and General Clothing Provision, since those two terms represent distinct service concepts.

Double indexing involves using terms from either the same branch of the Taxonomy (“vertical” or “intrabranch” double-indexing) or from different areas of the Taxonomy (“horizontal” or “interbranch” double-indexing) to index the same activity.

The basic rule to avoid double indexing is to think in terms of “one activity equals one service term”.

Ostensibly, double indexing is an attempt to ease searching for end users. In reality, the practice:

  • increases the workload of maintaining the resource database
  • produces inconsistent search results
  • provides an inaccurate picture of resources available in the community; and
  • confuses the documentation of problem/needs when a single call concerning a single issue may be documented as reflecting multiple different indexing terms.

Example of vertical double-indexing

Having accurately indexed a program under Job Banks (ND-3500.3500-340), a Resource Specialist decides to also assign higher-level terms on the same branch of the Taxonomy such as Job Information (ND-3500.3500) and Job Finding Assistance (ND-3500). Thus, indexing the program with three service terms:

Job Finding Assistance (ND-3500)

Job Information (ND-3500.3500)

Job Banks (ND-3500.3500-340)

The problem is that Job Information is a broader term than Job Banks, and Job Finding Assistance is an even broader term and they are being used to represent the same activity provided by the organization.

The recommended practice is to always index a resource using the most specific service term available (within the customized version of the Taxonomy used by that particular I&R) that accurately and completely represents the service being offered.

Example of horizontal double-indexing

A local library offers a children’s reading program during the summer. The Resource Specialist indexes with the most appropriate term available:

Children's Reading Clubs (TJ-4500.1500-450)

Thinking that people might also search for the program using the words “literacy” and “books”, the Resource Specialist also indexes the program with additional service terms from other branches of the Taxonomy:

Book Readings (TA-3000.0900)

Literacy Programs (HH-4500)

Unfortunately, reading the definitions of the two new terms reveals that they don’t reflect program that’s being indexed. Only the term originally chosen accurately reflects it, and only that term should be used to index it.

What double indexing is NOT

Note that double indexing only happens when multiple service terms are being used to index a specific service concept. It’s not considered to be double indexing when:

  • one or more target terms are linked to a service term to focus the indexing
  • a modality term is linked to a service term to focus the indexing
  • both an organization/facility type term and a service term are used to index the same database record.

All three of those are acceptable indexing practices.

Example of using a facility term and a service term

A Resource Specialist indexing a community clinic uses the organization/facility type term Community Clinics LN-1500 (“Consumer-based ... outpatient facilities that provide basic health care including physical examinations, immunizations, family planning, nutrition assistance and diagnosis and treatment of common ailments... “).

However, there are other programs in the resource database that specifically offer immunizations but not the other services typically offered by community clinics. Those service records have already been indexed using the term Immunizations (LT-3400). So while searching the resource database under the Immunizations term retrieves those latter records, it wouldn’t retrieve the program records indexed under the organization/facility type term Community Clinics.

Consequently, it is entirely appropriate to index the new community clinic program under both the service term and the organization/facility type term:

Immunizations (LT-3400)

Community Clinics (LN-1500)

Finally, it should be recognized that in many cases, a Resource Specialist can avoid the temptation of double indexing by requesting that an additional Use Reference or See Also Reference be added to the service term, and/or that a term definition be clarified or enhanced.

Note that some I&R software programs have “roll-down” features. This means that someone doing a keyword search for the term Job Information (ND-3500.3500) should be presented with all of the lower level terms that have been used in that branch, including Job Banks (ND-3500.3500-340). These features make the double indexing even more redundant.