As our society has become increasingly data dependent, statistics education has emerged as a field of study. Research has focused on statistics course content outcomes, showing most students struggle with statistical concepts, including variation and the standard deviation. Variation is a foundational concept in statistics. Without a firm grasp of the concept of variation, other central statistical concepts would be difficult to understand. Thus, it is imperative to understand how students solve statistical problems and develop conceptual understanding of variation in statistics. This study was designed to gain insight into the reasoning and procedural strategies of introductory statistics students as they solved standard deviation problems. The similarities and differences of proficient and non-proficient statistics problem solvers were explored. The characteristics of the thought processes of proficient problem solvers who demonstrated conceptual understanding were examined. In addition, this research inquired into students' ability to recognize multiple representations of the same data and to translate between representations. Eighty-six college level introductory statistics students completed an original survey designed specifically for this study. Eleven students and the course instructor were interviewed. Analysis of the data from the surveys and--interviews focused on students' reasoning and procedural strategies, their ability to recognize multiple representations of the same data, and the ability to translate between representations of data. Analysis revealed proficient students' problem solving strategies centered on knowledge types, the development of structural awareness, and the ability to recognize and translate data in multiple modes. Language fluency and the ability to work with multiple representations emerged as critical indicators of statistical literacy and conceptual understanding. Further research may be focused on instructional methods that include problem solving opportunities with data presented in multiple modes, translation between modes, and the process of developing language fluidity. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]