The LOINC committee approved inclusion of standardized assessment measures (e.g., survey instruments) with version 1.0p. Representing the observations in these assessments within LOINC required a modest extension of the System axis to include aggregate units of analysis, such as ^family, and storage of additional attributes within the LOINC database. Bakken[^1] provides a detailed description of the methodology for inclusion and evaluation into LOINC and the extensions to the LOINC axes.
The initial corpus of material represented in LOINC came from standardized nursing assessment instruments. We have since expanded the content to cover standardized assessment instruments in many other domains. As we have added content, we have iteratively refined our modeling. Vreeman et al have published a summary of our approach and its evolution.[^2]
[^1]: Bakken S, et al. Evaluation of Clinical LOINC (Logical Identifiers, Names, and Codes) for Terminology Model for Standardized Assessment of Measures. JAMIA 7:2000; 529-538. Pubmed: 11062226.
[^2]: Vreeman DJ, McDonald CJ, Huff SM. LOINC® – A Universal Catalog of Individual Clinical Observations and Uniform Representation of Enumerated Collections. Int J Funct Inform Personal Med. 2010;3(4):273-291. Epub 2011 May 23. PubMed: 22899966.