**Intraclass correlation coefficient / reliability study**

This function calculates the intraclass
correlation coefficient (ICC) using the methods described by Shrout, P.E., and
Fleiss, J.L "Intraclass correlations: uses in assessing rater
reliability," *Psychological Bulletin*, 1979, 86, 420-428.

There are six intraclass correlations:

ICC(1,1): used when each subject is rated by multiple
raters, raters assumed to be randomly assigned to subjects, all subjects have
the same number of raters.

ICC(2,1): used when all subjects are rated by the same
raters who are assumed to be a random subset of all possible raters.

ICC(3,1): used when all subjects are rated by the same
raters who are assumed to be the entire population of raters.

ICC(1,k): Same assumptions as ICC(1,1) but reliability
for the mean of k ratings.

ICC(2,k): Same assumptions as ICC(2,1) but reliability
for the mean of k ratings.

ICC(3,k): Same assumptions as ICC(3,1) but reliability
for the mean of k ratings. Assumes additionally no subject by judges
interaction.

**Method used for each correlation coefficient is as
below:**

ICC(1,1): |
One-way random
single measures |

ICC(1,k): |
One-way random
average measures |

ICC(2,1): |
Two-way random
single measures (Consistency/Absolute agreement) |

ICC(2,k): |
Two-way random
average measures (Consistency/Absolute agreement) |

ICC(3,1): |
Two-way mixed
single measures (Consistency/Absolute agreement) |

ICC(3,k): |
Two-way mixed
average measures (Consistency/Absolute agreement) |

**A sample screen shot of input window:**

Your data
could be organized so that each class has one line (one record) or multiple
lines. You can specify the data structure, and then select the method to
calculate the desired ICC.

**Sample output and explanation:**

Intraclass
correlation coefficient

icc.lme LCL ICC1 UCL

BMI
0.217001593 0.13987535 0.20907559 0.28579992

SBP
0.061762465 -0.02357091 0.03137998
0.09617033

DBP
0.002549532 -0.07823121 -0.03037675 0.02726936

icc.lme: intraclass correlation computed using
one way random effect model

ICC1: The intraclass correlation coefficient 1

ICC1: intraclass correlation computed using
one way ANOVA

LCL, UCL: 95%CI of intraclass correlation
computed using one way ANOVA

ICC from random effect model should be equal
an ICC from a one-way ANOVA only when the data are balanced (equal group sizes
for all groups and no missing data).

The icc.lme should be a more accurate measure
of ICC in all other instances.