Applications of traditional unidimensional item response theory models to passage-based reading comprehension assessment data have been criticized based on potential violations of local independence. However, simple rules for determining dependency, such as including all items associated with a particular passage, may overestimate the dependency that actually exists among the items. The current study proposed a more refined method based on cognitive principles and substantive theories to determine those items that pose a threat. Specifically, the use of common necessary information from text was examined as a contributor of local dependence. Cognitively similar item pairs, those with connected necessary information, had higher local dependence values than item pairs with no connected necessary information. Results suggest that focusing on necessary information may be useful to some extent for understanding and managing item dependence for passage-based reading comprehension tests.