### 4.2 Linear regression

If there is likely to be a causative relationship between two variables, such that the value of one variable determines most or all of the value of the second, a linear regression can be carried out. Again, a scatter plot is used to explore the relationship. The independent variable (commonly denoted x) is shown on the horizontal axis of the plot, whilst the dependent variable (denoted y) is shown on the vertical axis. If the calculated regression is significant, the fitted line should be added to the scatter plot (Fig. 10).

**Figure 10.** Scatter plot with fitted regression line