Which is an example of interval data?

• A. Weight in kilograms
• B. Temperature in Celsius
• C. Blood pressure ratio
• D. Age in years

Answer: (B)

Interval data are measurements where the difference between values is meaningful and consistent, but there is no true zero that indicates “none” of the quantity. On the Celsius scale, equal degree steps correspond to equal changes in temperature, so 10°C and 20°C differ by the same amount as 20°C and 30°C. However, zero degrees Celsius does not mean there is no temperature at all; it’s an arbitrary point. Because of that, you can add or subtract temperatures, but you cannot meaningfully say one temperature is twice another.

Weight in kilograms and age in years, as well as blood pressure in mmHg, are on ratio scales: they have a true zero and meaningful ratios (for example, 20 kg is twice 10 kg, and a 0-year age would mean no age). Therefore they aren’t interval data.