Statistical Aspects of Variability
Consider a pharmaceutical process producing paracetamol tablets, for which the weight of the active ingredient (nominally 500 mg per tablet) is one of the variables to be controlled. Suppose that the process is stable and the ingredient weights of 200 tablets are measured to the nearest gram and grouped in suitable classes of 5mg
width, giving the results shown in this table.
These results are now presented as a histogram. Notice that the dashed lines which join the mid-points of the classes form a profile which is roughly bell-shaped.