Hi Pamela,
This won’t be a satisfying answer, but it really just comes down to the resource you’re looking at. The ANPT used a 2005 study of healthy adults (ages >75 years) to come up with their recommendation. The gait speed chart in the NCS Advantage lecture used the 2009 Fritz and Lusardi article theorizing that gait speed is the sixth vital sign. Knowing that there is variability depending on the study, population age, diagnoses considered, etc. and having a general idea of interpreting gait speed should be sufficient for NCS exam purposes.
