This document discusses factors that affect the difficulty of reading tests and texts. It examines how language, question types, testing of skills, grammar, vocabulary, background knowledge and text length can influence reading assessments. It also explores the role of grammar and vocabulary in reading tests, and whether dictionaries should be allowed. Research has found that vocabulary accounts for most variance in reading performance, but it may measure prior knowledge rather than just lexical skills. The transfer hypothesis suggests limited language proficiency can hinder transferring reading ability between languages.