INTRACLASS CORRELATION COEFFICIENT(ICC)
the historical approach to reliability involved the use of that it doe Chapter 5 we discussed the problems with approach, incorrelation coefficients. In measure of agreement, but only covariance. Correlations are reliability coefficients because they are bivariate; that is, onl also limited as not possible assess the simultaneous ings or can be correlated at one time. It is to aspects of reliability of more than two raters or the relationships among different bility, such as raters, test forms, and testing occasions. As these are often important el ments in reliability testing, correlation does not provide an efficient mechanism f evaluating the full scope of reliability.
Another objection to the use of correlation as a measure of reliability is based on th statistical definition of reliability; that is, correlation cannot separate out variance com ponents due to error or true differences in a data set. Therefore, the correlation coefficient is not a true reliability coefficient. It is actually more accurate to use the square of the cor relation coefficient(the coefficient of determination) for this purpose, because r reflects how much variance in one measurement is accounted for by the variance in a second measurement(see Chapter 24 This is analogous to asking how much of the total ance in a set of data is shared by two measurements(the"true" variance) and how much is not shared(the error variance). If we could correlate true scores with observed scores in a set of data, the square of the correlation coefficient would be the reliability coefficient. We can confirm this interpretation using the data from Table 26.1A. For the correlation between observed and true scores, Therefore
To overcome the limitations of correlation as a measure of reliabili some researchers have used more than one reliability index with single study. For instance, in test-retest situation or a rater reliability study, both correlation and a t-test can be performed to assess consistency and average agreement between the data sets. This strategy does address the interpretation of agreement
INTRACLASS CORRELATION COEFFICIENT(ICC) the historical approach to reliability involved the use of that it doe Chapter 5 we discussed the problems with approach, incorrelation coefficients. In measure of agreement, but only covariance. Correlations are reliability coefficients because they are bivariate; that is, onl also limited as not possible assess the simultaneous ings or can be correlated at one time. It is to aspects of reliability of more than two raters or the relationships among different bility, such as raters, test forms, and testing occasions. As these are often important el ments in reliability testing, correlation does not provide an efficient mechanism f evaluating the full scope of reliability. Another objection to the use of correlation as a measure of reliability is based on th statistical definition of reliability; that is, correlation cannot separate out variance com ponents due to error or true differences in a data set. Therefore, the correlation coefficient is not a true reliability coefficient. It is actually more accurate to use the square of the cor relation coefficient(the coefficient of determination) for this purpose, because r reflects how much variance in one measurement is accounted for by the variance in a second measurement(see Chapter 24 This is analogous to asking how much of the total ance in a set of data is shared by two measurements(the"true" variance) and how much is not shared(the error variance). If we could correlate true scores with observed scores in a set of data, the square of the correlation coefficient would be the reliability coefficient. We can confirm this interpretation using the data from Table 26.1A. For the correlation between observed and true scores, Therefore To overcome the limitations of correlation as a measure of reliabili some researchers have used more than one reliability index with single study. For instance, in test-retest situation or a rater reliability study, both correlation and a t-test can be performed to assess consistency and average agreement between the data sets. This strategy does address the interpretation of agreement
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