A method of evaluating a standard uncertainty from measured data, typically the experimental standard deviation of n repeated readings, divided by the square root of n when the mean of those readings is reported. Ten readings with s = 3 µV give a standard uncertainty of the mean of about 0.95 µV with 9 degrees of freedom. The label describes how the number was obtained, not whether the underlying effect is random or systematic.
Type A on the repeats came out at 0.4 µm with nine degrees of freedom, it's not the big hitter.
Rookies equate Type A with random and Type B with systematic; the split is about evaluation method, and a Type A number can describe a systematic effect.
Also heard as
- Type A
- Type A uncertainty
Do not mix it up with
- Type B evaluation: Type B uses information other than fresh repeated data, such as certificates and specs; Type A comes from statistics on your own repeated readings.
Related terms
Type B evaluation
Sizing an uncertainty component from existing knowledge such as certificates, specs or resolution, with no new repeat data.
Standard deviation
The usual measure of scatter in a set of values, the square root of the average squared deviation from the mean.
Degrees of freedom
A count of the independent information behind an uncertainty estimate, showing how reliable that estimate is.
Repeatability
How tightly readings bunch when one person repeats a measurement with the same setup, in one place, in one short sitting.
Standard uncertainty
Uncertainty expressed as one standard deviation, the common currency for combining uncertainty components.