Precision is repeatability. Precision indicates how well a method or instrument gives the same result when a solitary sample is tested repeatedly. Precision actions the random error the a method, i beg your pardon is the scatter in the data. Precision go not suggest that an tool is reporting the correct result; i m sorry is accuracy.
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Two varieties of precision space measured; within run and between run. Within operation precision gives an confident estimate of the expected daily performance that a an approach or instrument since there is minimal opportunity for operating problems to adjust during a solitary analytical run. Within operation precision, should be evaluated and also accepted before proceeding with much more comprehensive studies.
Quality manage material is accessible commercially. At least two, and also sometimes three, concentrations of quality regulate material must be run for each analyte. Concentration of the analyte in the quality control samples need to be as close as feasible to the upper and also lower medical decision points. These decision points can represent the upper and lower referral values or country recommended decision points.
Clinical Laboratory criter Institute proposal running 2 levels of quality regulate material 3 times per operation for five different runs, offering 15 replicates of each level. Most in vitro diagnostic providers use this protocol when they install a brand-new instrument in a clinical laboratory.
Some laboratories think that a great precision examine should incorporate 20 to 50 replicates. The larger the number of replicates, the more confident you can be in the precision results. Because that example, if the true SD that a method is 1.00, a precision estimate based upon 20 replicates might range from 0.76 to 1.46. The precision estimate based on 50 replicates is narrower, varying from 0.84 to 1.24.
Mean, conventional deviation (SD), and also coefficient of sport (CV) are calculated because that each level using a spreadsheet.Mean is the average value, i beg your pardon is calculated by adding the results and dividing through the total number of results.SD is the main measure the dispersion or sports of the separation, personal, instance results about the mean value. The easiest means to calculate SD is usage the statistical tools present in a spreadsheet such together Excel. The greater the imprecision, the larger the standard deviation will certainly be. For numerous analytes, SD varies v sample concentration. Using glucose as an example, one SD of 10 for a 400 mg/dL sample suggests very an excellent precision, yet an SD of 10 for a 40 mg/dL sample represents very poor precision.CV is the SD expressed as a percent the the average (CV = conventional deviation/mean x 100). The greater the conventional deviation, the higher the percentage of the median it becomes and the greater the %CV.The 95% confidence interval for SD is a measure up of the precision of the precision estimate. The broad of the trust interval relies on the number of samples analyzed and also the intrinsic SD of the method.
If an tool or method has great precision, 95% of values should loss within 2 standard deviations of the mean. That means that no an ext than 1 that the 20 results have to fall outside of 2 traditional deviations.
Calculated SD and CV must be contrasted to the manufacturer"s published statistics. If the obtained results are higher than the manufacturer"s claim, an investigation must it is in undertaken prior to proceeding additional with the technique evaluation.
Below is an instance of within run precision because that Level 1 quality regulate material because that sodium. The QC material is recurring 30 times and the adhering to results space obtained: 110, 110, 111, 111, 111, 111, 111, 111, 111, 111, 111, 111, 111, 112, 112, 112, 112, 112, 112, 112, 112, 112, 112, 112,112,112, 113, 113, 113, and also 113.
The amount of the thirty results is 3346. The typical is calculation by splitting 3346 by 30, which offers a result of 111.6. SD is 0.8 and also CV is 0.72%. The 95% trust interval is the average +/-2SD or 110.0 – 113.2.
Between run precision is a much better indicator the a method’s overall precision 보다 within run precision since it procedures the quantity of arbitrarily error natural in the technique from day to day. In between run precision is influenced by numerous variables together as transforms in operators, reagents and also ambient operating conditions.
Concentration the the analyte in quality manage samples need to be as close as feasible to the upper and also lower clinical decision points (usually the reference limits). Between run precision should be evaluated end at the very least 20 days using at the very least 2 reagent lots. The mean, traditional deviation, and also coefficient that variation space calculated for each level.
The conventional deviation derived during day-to-day replication studies is supposed to be greater than the conventional deviation the within operation studies. The preferably allowable between run typical deviation is a matter of judgment. Generally, it must be much less than full allowable error (see appendix B).
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Acceptable CVs have to be defined for every analyte based upon medical significance. Generally, precision have to be equal to or less than one fifty percent of the in ~ subject organic variation. Desirable precision levels for some usual chemistry analytes space summarized in the adhering to table.