Dependability of measurement in counseling psychology: An introduction to generalizability theory

Classical approaches to the assessment of reliability neglect to take into account multiple sources of error and to consider diverse measurement conte xts. Generalizability theory (GT) offers a flexible framework for assessing dependability of measurement. With GT investigators can estimate the total proportion of variance in ratings that is due to error rather than focusin g on one source of error at a time. Simultaneous consideration of multiple sources of error allows investigators to assess the overall impact of measu rement error in terms of attenuation of study findings and reduction of sta tistical power Estimation of variance components allows for flexible applic ation of findings to a variety of possible future research designs. Illustr ative analyses demonstrate the special advantages of GT for planning studie s in which observer ratings will be used.