Simple precision determines the variation of a method observed for a single run (within a device or laboratory).
The requirements of the test are:
Data in existing Excel worksheets can be used and should be arranged in the List dataset layout. The dataset must contain at least one continuous scale variables containing the observations for a run of the method.
When entering new data we recommend using New Dataset to create a new precision dataset.
To start the precision analysis:
Excel 97, 2000, 2002 & 2003: Select any cell in the range containing the dataset to analyse, then click Analyse on the Analyse-it toolbar, click Precision then click Simple.
The report shows the total number of observations analysed. The Concentration (if the pre-assigned concentration was specified) and the Mean concentration of all replicates is shown. If the pre-assigned concentration is not known the mean is used as an estimate of the true concentration.
The SD, a confidence interval showing the range likely to contain the true precision SD, and CV are shown.
A precision plot (see below) shows the standardized observations from the mean. Observations outside ±4 SDs should be investigated as potential outliers.
Precision can be compared against a performance goal. Allowable precision can be specified in absolute units of the analyte, as a percentage of analyte concentration, or as a combination of the two in which case the larger of the absolute and percentage concentration is used.
To compare precision against a goal:
The precision goal, calculated from the imprecision specification and the concentration level, and a hypothesis test to test if the observed precision is within the goal are shown. If the p-value is significant the observed precision is outside the goal.
Precision can be compared against a random error% of a total allowable error goal. Total allowable error can be specified in absolute units of the analyte, as a percentage of analyte concentration, or as a combination of the two in which case the larger of the absolute and percentage level is used.
To compare precision against a random error% of total allowable error:
The precision goal, calculated from the random error specification and the concentration level, and a hypothesis test to test if the observed precision is within the goal are shown. If the p-value is significant the observed precision is outside the goal.
