There are four levels of measurement of data listed below in increasing order:
Nominal
Ordinal
Interval
Ratio
The nominal level of measurement is the lowest level that deals with names, categories and labels. It is a qualitative expression of data e.g Colors of eyes, yes or no responses to a survey, and favorite breakfast cereal all deal with the nominal level of measurement.
Data at this level can't be ordered in a meaningful way, and it makes no sense to calculate things such as means and standard deviations.
