This chapter gives an overview of different approaches to data collection. Three methods of comparative variable studies are presented in detail and illustrated with examples from the early history of printing: intratextual, intertextual and cross-textual variable analyses. Intratextual variable analysis investigates the frequency and range of spelling variants in a single text copy and is particularly useful for the detection of possible internal factors that trigger the choice of a variant. The intertextual analytical method compares the results of two or more intratextual investigations, for example with respect to different external determinants such as time and place. The third method, cross-textual variable analysis, compares the spelling variants of different versions of the same text, and is concerned with alterations from one version to the other in order to detect a pattern of deliberate changes. The advantages and disadvantages of the three methods are considered in the chapter, and their inherent theoretical premises are discussed. The author shows that data collection and interpretation are closely intertwined, and also that the chosen approach prestructures the data and leads to preferences for specific interpretations.