CTT reliability

Question 1

Ways to enterpret reliability

Answer 1

One distinction is whether to aproach in terms of proportion of variance or in terms of correlation

Second is to approach in terms of observed scores as related to true scores or to measurement error

Question 2

Ratio of true score variance to observed score variance

Answer 2

Rxx is frames by devideing the signal by the signal+noise. It gives you the proportion of variance that is attributable to the true score (signal) variance.

The max is Rxx=1.0 but that won’t happen. Generally .7-.8 is acceptable

Question 3

Lack of error variance

Answer 3

Same as ratio of true score variance, but here it divides the error variance by the observed variance. this is substracted from 1 (Rxx = 1 - (se2/so2).

the percentage will indicate the amount of var explained by the true scores

Question 4

Squared correlation between observed an true

Answer 4

Index of reliability shows correlation between observed true scores. If you square this you get the reliability coeff.

Question 5

Lack of (Squared) correlation betw observed and error

Answer 5

Same as squared correlation but than 1-St2