Reliability investigates to what extend measurements/scales are internally consistent (internal consistency reliability) as well as results of the scale are more or less identical if the scale is repeatedly administered (test-retest reliability).
The internal consistency reliability - measured with Cronbach’s Alpha - was good with r= 0.74 for the total scale (sample n=230 Italian women). All but one of the domains had acceptable reliability coefficients: The values were 0.73, 0.73, 0.78, 0.81, and 0.53 for the subscales “PSYCH”, “HORM”, “MENS”, “SEX”, and “ABDOM”, respectively. The alpha of the latter domain should be re-analyzed in patient groups with medically confirmed diagnosis (self-reported in this study).
The results were confirmed in the German validation study (n=108): The Cronbach’s alpha was again good with r= 0.82 for the total scale, and the for the subscales “PSYCH”, “HORM”, “MENS”, “SEX”, and “ABDOM” 0.77, 0.69, 0.92, 0.83, and 0.53, respectively. Altogether, we consider an internal consistency reliability of over 0.7 as sufficiently good.
The test-retest reliability was determined in the framework of the German validation study in 2007 (n= 108). A pretty good reliability was observed for the total score (r= 0.92), and for the five domain scores: The test-retest coefficients were r=0.83, r=0.85, r= 0.93, r=0.72, r=0.62 for the subscales “PSYCH”, “HORM”, “MENS”, “SEX”, and “ABDOM”, respectively. Altogether, the result of the test-retest reliability study can be summarized as satisfactory, i.e. confirming what has been shown in the two studies with analyses of Cronbach’s alpha.