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help for ^icc23^
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^Calculation of ICC Models 2 and 3^
^---------------------------------^
.^icc23^ , MOdel(#) LEvel(#)
^Description^
^-----------^
^icc23^ computes the intra-class correlation for random effects models based on repeated
measures ANOVA. These models are ICC[2,1], ICC[2,k], ICC[3,1], and ICC[3,k], as described
by Shrout and Fleiss, 1979 (see reference below). (For the ICC[1,1] and ICC[1,k] models
based on a one-way ANOVA, see @loneway@). ^icc23^ runs a repeated measures ANOVA to derive
the appropriate estimates and degrees of freedom. In the event there is a significant F-test
for the ^classvar^ (e.g., a significant differernce among raters), the program will provide
the p-value from the ANOVA table.
Data must be in the "long" format. If not, use the @reshape@ command to reconfigure the data.
Four types of ICC models are considered:
ICC[2,1]: reflects the case where the same group of subjects is rated by k raters,
interest is in the reliability of individual scores. In this model, raters
are considered a representative sample of a population of similar raters. This
model is a two-way random effects model.
ICC[2,k]: is the same approach as ICC[2,1] above, but interest is in the reliability
of the MEAN score, rather than among single observations.
ICC[3,1]: reflects the case where the same group of subjects is rated by k raters,
interest is in the reliability of individual scores. In this model, the only
raters of interest are those participating in the study (e.g., there is no
intention of generalizing the raters' scores to a larger population of raters).
This model is considered a "mixed" model (subjects are random, raters are fixed).
ICC[3,k]: is the same approach as ICC[3,1] above, but interest is in the reliability
of the MEAN score, rather than among single observations.
Three inputs are required:
dv is the dependent variable
classvar the class variable refers to factor that is repeated within subjects, e.g., raters,
devices, time points, etc., e.g., the variable which would be entered as the
repeated() variable in the ANOVA option.
within_var refers to the "within subject" variable, e.g., subjects being assessed
^NOTE: The order of entry of the variables is critical!^
^Options^
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^MO^del(#) refers to the type of model to be estimated. ICC model 2 is the default (
producing ICC[2,1] and ICC[2,k] estimates).
^LE^vel(#) the degree of precision of the confidence interval, entered as a decimal.
The default is 95%, i.e., level(.95)
Examples
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For ICC[2,1] and ICC[2,k]: Two-way random effects (Subjects and raters are considered to be
sampled from larger populations); 95% CIs are assumed.
^.icc23 score rater person_id^
For ICC[3,1] and ICC[3,k]: Two-way mixed model: Subjects are random, but raters are fixed
(i.e., the raters are not considered a sample -- they are the
only raters of interest); 90% CIs are requested.
^.icc23 score rater person_id, model(3) level(.90)^
References
----------
Shrout PE, FLeiss JL. Intraclass correlation: uses in assessing rater reliability. Psychol
Bull, 1979; 86: 420-428.
Portney LG, Watkins MP. Foundations of Clinical Research: Applications to Practice (2nd ed.).
Prentice-Hall, Inc: Upper Saddle River, NJ., 2000.
Author
------
Paul F. Visintainer, PhD
Baystate Health System
Springfield, MA 01089
visint46@gmail.com
Luis C.Orozco, MD, MSc
Facultad de Salud
Universidad Industrial de Santander
Colombia
lcorovar@gmail.com
Also see
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Manual or on-line help for: @loneway@, @reshape@, @iclassr@, @iclassr2@