Recent research into students' reasoning about variation refers specifically to notions of distribution that emerge. This paper reports on research where written responses, from tertiary introductory statistics students, were coded according to the level of consideration of variation. A hierarchy of reasoning about distribution is proposed, based on the notions of distribution that were evident in these responses. The hierarchy reflects students' progression from describing key elements of distribution to linking them for comparison and inference. The proposed hierarchy provides researchers with an emerging framework of students' reasoning about distribution. The research also highlights that educators need to be aware that, without a well developed consideration of variation, students' ability to reason about distribution will be hampered.