Abstract. Using two meta-analytic datasets, we investigated the effect that two scale-item characteristics – number of item response categories and item response-category label format – have on the reliability of multi-item rating scales. The first dataset contained 289 reliability coefficients harvested from 100 samples that measured Big Five traits. The second dataset contained 2,524 reliability coefficients harvested from 381 samples that measured a wide variety of constructs in psychology, marketing, management, and education. We performed moderator analyses on the two datasets with the two item characteristics and their interaction. As expected, as the number of item response categories increased, so did reliability, but more importantly, there was a significant interaction between the number of item response categories and item response-category label format. Increasing the number of response categories increased reliabilities for scale-items with all response categories labeled more so than for other item response-category label formats. We explain that the interaction may be due to both statistical and psychological factors. The present results help to explain why findings on the relationships between the two scale-item characteristics and reliability have been mixed.