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Used to compare the degree of consensus between
raters (inspectors) in, for example, Measurement
Systems Analysis. It uses a contingency table
approach.
Two raters inspect 150 parts independently and
make the following determinations:
| |
|
|
Bret |
|
| |
|
Reject |
Accept |
Total |
| |
Reject |
20 |
19 |
39 |
| Alice |
Accept |
1 |
110 |
111 |
| |
Total |
21 |
129 |
150 |
The expected values in each cell would be:
| |
|
|
Bret |
|
| |
|
Reject |
Accept |
Total |
| |
Reject |
5.46 |
33.54 |
39 |
| Alice |
Accept |
15.54 |
95.46 |
111 |
| |
Total |
21 |
129 |
150 |
These are the values that would give the same
totals if the determinations were made by pure
chance and is calculated from:
(row total x column total)/overall
total
The Kappa statistic is calculated from:
where:
| Actual |
the number of times the
appraisers agreed (110 + 20 = 130) |
| Expected |
the number of times they
would have agreed by chance (5.46 + 95.46) |
| Trials |
the number of trials |
The value of Kappa will be between 0 and 1.
If the results were made by chance, neither rater
showing judgment the value would be zero. If the
raters were in perfect agreement, the number of
agreements would equal the number of trials and
Kappa would be 1.
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