Levels of Measurement
The Four Horsemen of Measurement - hear their names: Nominal, Ordinal, Interval, Ratio.
“The Four Horsemen whose Ride presages the end of the world are known to be Death, War, Famine, and Pestilence. But even less significant events have their own Horsemen. For example, the Four Horsemen of the Common Cold are Sniffles, Chesty, Nostril, and Lack of Tissues; the Four Horsemen whose appearance foreshadows any public holiday are Storm, Gales, Sleet, and Contra-flow.” — Terry Pratchett, Interesting Times: The Play
How can phenomenons be measured?
There are four data measurement scales: nominal, ordinal, interval and ratio. Simply these are ways to sub-categorize different types of data. It’s important to know what type of data you have, because it heavily influences the choice of statistics and graphical representation.
The first characterization is whether the data is numerical or not:
If you have got numerical data, you have got quantitative data.
If you do not have numbers, you have got qualitative data.
Let’s move on to the description of qualitative data …