Table 8.

Limitations of Database--Nationwide Inpatient Sample from years 2001 to 2010.

Category	Limitation
Disease Severity	Cannot indicate severity of pre-operative CSM Cannot identify or weigh differently the variation in neurologic function Nurick, Frankel, JOA, or Ducker Motor Index quantitative assessment of neurologic involvement unavailable Presence or absence of myelomalacia is not controlled for
Surgical Approach	Laminoplasty versus laminectomy differentiation using ICD-9-CM codes is difficult NIS database does not list the presence nor the type of spinal instrumentation NIS database pools together one-level surgeries with multi-level, including 5-level, operations. The number of surgical vertebral levels has an impact on outcomes and it is expected that the combined anterior-posterior group has the highest number of multilevel cases.