This website is for students following the M.Sc. in Evidence Based Practice at the University of York.

183 students were observed twice by different student observers. These measured height (mm), arm circumference (mm), head circumference, and pulse (beats/min) and recorded sex and eye colour. They entered these into a computer file. Eye colour and sex were entered as numerical codes.

The following table shows sex as recorded by two observers:

Sex recorded by first observer | Sex recorded by second observer | Total | ||
---|---|---|---|---|

female | male | |||

female | 118 | 1 | 119 | |

male | 1 | 63 | 64 | |

Total | 119 | 64 | 183 |

This is the output from SPSS 16, where kappa is a statistic available from crosstabs:

Symmetric measures | |||||
---|---|---|---|---|---|

Value | Assym. Std. Error ^{a}
| Approx T ^{b } | Approx. Sig. | ||

Measure of agreement | Kappa | 0.976 | 0.017 | 13.203 | .000 |

N of Valid Cases | 183 | ||||

a: Not assuming the null hypothesis. b: Using the asymptotic standard error assuming the null hypothesis. |

This is the output from a Stata command for Cohen's kappa:

. kap sex1 sex2 Expected Agreement Agreement Kappa Std. Err. Z Prob>Z ----------------------------------------------------------------- 98.91% 54.52% 0.9760 0.0739 13.20 0.0000

Note that SPSS uses the standard error shown by Stata to calculate the T statistic, not the one SPSS prints.

What is meant by “Agreement” and “Expected agreement”?

**
Question 2:
**

What does kappa mean and what can we conclude?

**
Question 3:
**

What is “Z” from Stata, T from SPSS?

“Prob>Z” in Stata and "sig" in SPSS is the P value. What is it testing?

**
Question 5:
**

How is it possible for kappa to be less than 1.00 for sex?

Back to Measurement in Health and Disease index.

This page maintained by Martin Bland.

Last updated: 21 July, 2008.