Frequency vs. intensity: which should be used as anchors for self-report instruments?

BACKGROUND: The aim of the present study was to investigate the usability of verbal rating scale anchors in patients suffering from a depressive episode and whether differences between frequency or intensity scales could be determined. Frequency and intensity terms were evaluated concerning their interindividual congruency, intraindividual stability across time, and distinguishability of adjacent terms. METHODS: In a longitudinal design, 44 patients (age M=39.1, SD=15.2, 68.2% female) with a depressive disorder filled out several established questionnaires (e.g. BDI or SCL-90) and questionnaires containing frequency and intensity terms which should be indicated by the percentage of time or intensity that is reflected by each term at two different measuring times within one week. Data analysis contained t-tests for paired samples and effect sizes d according to Cohen. RESULTS: Intensity terms showed weaker intraindividual stability across time as compared to frequency terms. Participants were able to reliably distinguish four frequency and intensity terms at both measuring times. Overall congruency between patients was larger for intensity terms in comparison to frequency terms. CONCLUSIONS: The present results indicate that both frequency and intensity terms can be applied as verbal anchors for clinical self-report scales. However, if longitudinal assessment is intended, our results indicate that frequency terms should be used as they showed slightly greater stability across time. Generally, the present study suggests that no more than four different verbal anchors should be used together in rating scales as especially older patients and those with low lexical experience would not be able to reasonably differentiate more than these.