Figure 1. Flowchart representing literature search.

A total of 1410 references were identified via database searches of PubMed (MEDLINE) and ICL (Index to Chiropractic Literature). After the removal of duplicates and screening of titles and abstracts using inclusion/exclusion criteria, and the addition of six records identified from direct journal searching, a total of 142 records were sought for retrieval. Nine papers were excluded by mutual agreement (A. Haas and J. Chung) as follows: two papers did not offer quantitative outcomes measures; one paper did not clearly include chiropractic adjustment or manipulation in their methods; six papers did not report statistically significant changes and therefore did not meet inclusion criteria. The resultant final database contains 133 references mutually agreed upon by two investigators (A. Haas and J. Chung) as meeting the inclusion/exclusion criteria for the present study.