ABSTRACT
When analyzing and depicting data that involve relationships, we are often presented with data in pairs (X, Y pairs). In Figure 2.1, the optical density Y and the concentration X are the data pairs. When considering the relationship of two variables, X and Y, one variable can often be considered the response variable, which is dependent on the selection of the second or causal variable. The response variable Y (optical density in our example) is known as the dependent variable. The value of Y depends on the value of the independent variable, X (drug concentration). Thus, in the example in Figure 2.1, we think of the value of optical density as being dependent on the concentration of drug.
