a. Validity is a measurement concept that asks whether a measurement
system actually measures what it's supposed to (i.e., joint range of motion
in the case of goniometry)
b. Goniometric measurements can be invalid; usually because of poor
stabilization. (see positioning and
stabilization)
RELIABILITY
a. Reliability is a measurement concept that asks whether successive
measurements are consistent, repeatable or reproducible. Upper extremity
measurements are more reliable than lower extremity measurements.
1) intratester reliability (same tester on different occasions)- measurement
error should be less than 5 degrees