Analysis of relationship between dependent and independent variable
The following example deals with about 100 adults, in whom we have measured length (X-axis, the origin is not at 0 cm) and inspiratory vital capacity (IVC, Y-axis). It is intuitively clear that generally taller persons will have a larger IVC. Body dimensions will determine lung size, and not the other way around; hence length is the independent and IVC the dependent variable. Typically data cluster like a torpedo-like cloud of data points, as in the figure. We can fit a line by eyeballing, but there are formal statistical techniques to do this. What these techniques achieve is to describe how differences in the dependent variable can be explained by differences in the independent variable: we perform regression of y on x.