Figure 1.

Frequency of International Classification of Diseases, Ninth Revision (ICD-9) co-documentation with tobacco use codes. Each point represents a single ICD-9 code. Points to the right of the equal documentation line (indicated in white) have an increased frequency of co-documentation with an ICD-9 tobacco use code (eg, 300 more individuals had their code documented on the same day than those whose code was documented on different days). Points to the left of the center line have a reduced frequency of co-documentation with tobacco use codes.