We need to discuss this early in the process because many of the techniques we will be using later are dependent on level of measurement. Level of measurement is a characteristic of anything that we measure. If we ask people what their religious preference is, or how much they liked a movie or how many children there are in their family, then the answer they give will have a level of measurement. Strictly, there are four levels of measurement. However, for the statistics we will be doing, two of the levels of measurement are essentially the same.
Levels of measurement have an inherent order.
That is, they go from lower levels of measurement to higher levels of measurement. There are few requirements for the lowest level of measurement. As we move up the levels of measurement, more requirements are added. All of the characteristics of the lower levels of measurement are required in the higher ones. The lowest level of measurement is Nominal.