Further reading
US Military Data Repository (MDR) data dictionary: https://www.health.mil/Military-Health-Topics/Technology/Support-Areas/MDR-M2-ICD-Functional-References-and-Specification-Documents
SAS white paper, Guido's Guide to PROC FREQ – A Tutorial for Beginners Using the SAS® System by Joseph J. Guido, available here: https://www.lexjansen.com/nesug/nesug07/ff/ff07.pdf
Information about blood pressure categories from Harvard Health available here: https://www.health.harvard.edu/heart-health/reading-the-new-blood-pressure-guidelines
SAS white paper, Creating Statistical Graphics in SAS® 9.2: What Every Statistical User Should Know by Robert N. Rodriguez and Tonya E. Balan, available here: https://support.sas.com/resources/papers/proceedings/proceedings/sugi31/192-31.pdf.