Ordinarily, variables appear as columns and cases as rows in a data table. We display data, seeking patterns. The intuitive area principle guides the design of displays, devoting equal display area to equal amounts or values. For inPidual variables we display distributions and think about numbers of modes, skewness and symmetry, and the possibility of outliers. A standard of comparison is the Normal density.
Density curves formalize the idea of relative frequency from the vague area principle idea.
We summarize inPidual variables by finding their center and spread. For pairs of variables measured on the same inPiduals we make scatterplots and consider the direction, form, and squares lines and with residuals away from those lines. We next consider how good data arise, with particular attention to the role of randomization. We randomize experiments to reduce bias and minimize the effect of factors that we cannot control. We draw random samples so that they will represent the underlying population.