We present an analysis of two user strategies in interactive data analysis, based on an observational study of four researchers in the immunology domain. Screen captures, video records, interviews, and verbal protocols are used to analyze common procedures in this type of visual data analysis, as well as how these procedures differ among these users. Our findings present a case where skilled users can approach a similar problem with diverging analysis strategies. In the group we observed,

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... gies fell within two broad categories: within-graph analysis, in which a user generates a few graph layouts and interacts heavily within them, and between-graph analysis, in which a user generates a series of graphs and switches between them in sequence. Differences in strategies lead to distinct interaction patterns, and are likely to be best supported by different interface designs. We characterize these observed strategies and discuss their implications for scientific visualization design and evaluation.