Certified Pulmonary Function Technologist (CPFT) Practice Exam

Which of the following describes a measurement that is the same every time, but may not be correct?

1. Accuracy

2. Standard deviation

3. Precision

4. Linearity

The correct answer is: Precision

The concept of precision refers to the consistency and reliability of a measurement method, indicating that repeated measurements yield similar results even if those results are not necessarily close to the true value. In other words, precision is about the repeatability of results. Therefore, a measurement can be highly precise—repeatedly yielding the same value—while still being inaccurate or differing from the true value. For instance, if a scale consistently reads 5 pounds too high every time it is used, it is precise because it gives the same reading for the same weight each time, but it is not accurate since the true weight is different. This distinction is crucial in fields like pulmonary function testing, where consistent measurements are vital, but accuracy is equally important for correct diagnosis and treatment. In contrast, the other terms have distinct meanings: accuracy relates to how close a measured value is to the true value; standard deviation measures the variability of a set of data; and linearity refers to how well a method's results correspond to a known reference across a range of values. Each of these terms conveys different aspects of measurements, reinforcing the unique nature of precision.