Focus on Accuracy and Precision, and how to calculate the Accuracy and Precision of measurements.
Terms And Equations
Accuracy – How close a measurement is to the actual or expected value.
Precision – How close a set of measurements are to one another.
Error – The difference between the actual or expected value, and the measured value.
Absolute Error = Actual value – Measured value
Relative Error = (Actual value – Measured value) / (Actual Value)
% Error – Relative Error X 100%
Deviation – The difference between a measurement within a set and the mean of that set of measurements.
Deviation = Measurement - Mean
Average Deviation - The average of the Deviations of all measurements within a set.
Systematic Error – Error that impacts all or a large portion of measurements in a set uniformly, or by some type of trend.
Random Error – Error that occurs sporadically, without any sort of trend or predictability.
Offset error – is when a machine is not calibrated or set to measure zero, when the sample is at zero.
Multiplier error - is an equipment malfunction where it amplifies changes in readings, or has a diminished sensitivity to change.
Source: Chemistry Quick Review of Experimental Error. Anne Marie Helmenstine, Ph.D., About.com,http://chemistry.about.com/od/chemistryquickreview/a/experror.htm.