I understand that temperature is interval scale because it holds no true zero and can represent values below zero. But in case of body temperature it cannot go below a certain point and definitely not below zero. So in that case, will body temperature be a ratio scale?
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How/where will you use this? – user2974951 Aug 09 '21 at 07:46
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This question popped up in my mind while reading on levels of measurement. Everywhere temperature has been mentioned as an interval scale and the case of 0°C has been cited as an argument. – Harry Aug 09 '21 at 09:12
2 Answers
Any temperature, including body temperature, has a natural zero: $0$ K $(-273.15 °C)$. So, if you express it in Kelvins, it is ratio scaled. An object at 2000 K is twice as hot as an object at 1000 K.
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Distinguish the proper from the measurable: The human body temperature is not bounded. Imagine a body found buried under deep snow (brrrr!), its temperature is obviously below zero. It is a measurable body temperature, and the same applies for extremely high temperatures (although at some point it'll decompose so somewhere there is an upper bound).
A proper body temperature is bounded, whether you put the interval as 36-38°C for strictly proper or you set it to 34-42°C to include most conditions of illness (such as hypothermia).
For both cases (measurable and proper), as there is no real "true zero". We know a general lower bound on temperatures which is Kalvin's zero, −273.15 °C, but it is not feasible so this is not a ratio scale.
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