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	Accuracy v. Precision

Solution In the fields of science, engineering, industry and statistics, accuracy is the degree of conformity of a measured or calculated quantity to its actual (true) value. Accuracy is closely related to precision, also called reproducibility or repeatability, the degree to which further measurements or calculations show the same or similar results. The results of calculations or a measurement can be accurate but not precise; precise but not accurate; neither; or both. A result is called valid if it is both accurate and precise. The related terms in surveying are error (random variability in research) and bias (non-random or directed effects caused by a factor or factors unrelated by the independent variable).

Accuracy and precision are important terms in equipment recommendations and warrant some definition. Accuracy error is the systematic difference between the “true” and the measured value The accuracy of a spirometer system depends on a number of factors, including linearity and frequency response of the system or processor, sensitivity to environmental conditions, calibration, and adequacy of correction factors. Its precision depends on the signal/noise ratio and on the resolution (i.e, the minimal detectable volume or flow). Precision error, usually denoted reproducibility, is the numerical difference between successive measurements.

What can be done to assure the most accurate and precise pulmonary function test?

Equipment
1. Performance. Choose equipment that meets or exceeds the ATS/ERS Standards and has been properly validated. Check with the manufacturer for verification and contact independent testing laboratories for information on their spirometer validation studies.
2. Equipment Quality Control. Check that the equipment is functioning properly by checking the calibration and performing maintenance procedures at regular intervals.

Spirometric Results
1. Performance. Obtain the best possible results from subjects through appropriate subject preparation and coaching.
2. Calculations. Use calculation methods standardized by ATS/ERS for determining test results.
3. Acceptability. Use only results from maneuvers that are free from errors.
4. Reproducibility. Use results with minimal variability whenever possible.

Interpretation of Results
1. Reference values. Select reference values appropriate to the setting and ensure that the same values are used consistently.

Spirometry technicians play a critical role in obtaining accurate and precise results. They frequently have primary responsibility for seeing that quality assurance measures are carried out; selecting, preparing, and coaching subjects; and determining whether results are acceptable and reproducible. Therefore it is essential that these individuals receive comprehensive training in these areas.

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05 Dec 2008 09:23 AM

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