At a 90% confidence level, what is the precision measurement factor used in bone densitometry?

• A. 1.84 x precision
• B. 2.77 x precision
• C. 2.33 x precision
• D. 3.00 x precision

Answer: (C)

In bone densitometry, the precision measurement factor at a 90% confidence level is derived from statistical principles, specifically pertaining to the normal distribution. To achieve this confidence level, which indicates that we can be 90% certain that the true value lies within the computed range, a specific multiplier is utilized.

For a 90% confidence level, the corresponding z-score is approximately 1.645. When this z-score is translated into a precision factor for bone densitometry, it is often rounded to a more practical number for clinical use, which results in a commonly accepted value of 2.33. This factor essentially indicates how much variation can be expected in measurements and helps to establish a reliable confidence interval for test results.

Therefore, when a measurement is reported as "2.33 x precision," it reflects the multiplication of the standard deviation (precision) of the measurements to indicate the range within which we would expect the true bone density to lie with 90% confidence, making it the most accurate representation for this scenario.