Glossary

ISCD  International Society for Clinical Densitometry
This non-profit medical society dedicated to high quality in the field of bone densitometry.
DXA  Dual Energy X-ray Absorptiometry
This is the most common technology for measuring BMD of the spine, hip, or forearm.
ROI  Region of Interest
A portion of the skeletal site selected for BMD measurement, such as femoral neck or trochanter.
BMD   Bone Mineral Density
Expressed as g/cm2 when measured by DXA.
SD  Standard Deviation
This is calculated for the BMD values of each patient.
SD sq  Sum of SD sq Values
The total of SD sq values for 15 patients tested 3 times each, or 30 patients tested 2 times each.
N   Number of Patients
This is usually15 or 30 for precision testing.
Sum/n   Sum of SD sq Values Divided by the Number of Patients Tested
SqRT Square Root of Sum/n
PE    Precision Error
This may be expressed as RMS SD, CV, or %CV.  RMS SD is recommended.
RMS SD  Root Mean Square Standard Deviation
The standard deviation of the group, and the preferred method of expressing precision error, in g/cm2.
CV Coefficient of Variation
SD divided by the mean BMD.  Not advised for expressing precision error.
%CV   Percent Coefficient of Variation
CVx100%.  Not advised for expressing precision error.
CL Confidence Level
The ISCD recommends a 95% confidence level for establishing statistical significances for serial BMD testing.
LSC  Least Significant Change
This value is calculated by multiplying the precision error by 2.77 for a 95% confidence level.  For a BMD change to be considered statistically significant, it must equal or exceed the LSC.  LSC should be calculated with a new DXA instrument, and whenever it is moved to a new room or location.
FAQ Frequently Asked Questions
Click this link to view commonly asked questions about precision assessment and the precision calculator.

Last modified: December 30, 2012