Univariate Statistics 1. 2P does not equal M. 2. The wealthiest does not necessarily have 3 times the wealth of the 3rd wealthiest. True numbers are potentially continuous and in ascending sequence and the distance between any two units of value is equal.
Most interval scales are imperfect and tend to become ordinal or nominal at the extremes.
Always try for the highest possible scale, but recognize the limitations. Do not use mean X for a nominal scale and be aware of when you are 'stretching' a coding scheme. How many, how often, gaps, central tendency, dispersion and so forth. You will see why soon. A measure of central tendency most accurate for normal curves.