The difference between interval and ratio scales comes from their ability to dip below zero. Interval scales hold no true zero and can represent values below zero. For example, you can measure temperature below 0 degrees Celsius, such as -10 degrees.
Ratio variables, on the other hand, never fall below zero. Height and weight measure from 0 and above, but never fall below it.
An interval scale allows you to measure all quantitative attributes. Any measurement of interval scale can be ranked, counted, subtracted, or added, and equal intervals separate each number on the scale. However, these measurements don’t provide any sense of ratio between one another.
A ratio scale has the same properties as interval scales. You can use it to add, subtract, or count measurements. Ratio scales differ by having a character of origin, which is the starting or zero-point of the scale.
Interval-ratio scales comparison
Measuring temperature is an excellent example of interval scales. The temperature in an air-conditioned room is 16 degrees Celsius, while the temperature outside the room is 32 degrees Celsius. You can conclude the temperature outside is 16 degrees higher than inside the room.
But if you said, “It is twice as hot outside than inside,” you would be incorrect. By stating the temperature is twice that outside as inside, you’re using 0 degrees as the reference point to compare the two temperatures. Since it’s possible to measure temperature below 0 degrees, you can’t use it as a reference point for comparison. You must use an actual number (such as 16 degrees) instead.
Interval variables are commonly known as scaled variables. They’re often expressed as a unit, such as degrees. In statistics, mean, mode, and median can also define interval variables.
A ratio scale displays the order and number of objects between the values of the scale. Zero is an option. This scale allows a researcher to apply statistical techniques like geometric and harmonic mean.
Where you cannot imply that the temperature is twice as warm outside because it’s an interval scale, you can say you are twice another’s age because it’s a ratio variable.
Age, money, and weight are common ratio scale variables. For example, if you are 50 years old and your child is 25 years old, you can accurately claim you are twice their age.
Interval ratio scale measurements
Understanding the different scales of measurement allows you to see the different types of data you can gather. These differences help you determine the kind of statistical analysis required for your research.
Here is a brief description of the difference in interval and ratio levels of measurement:
The interval level of measurement classifies and orders a measurement. It specifies a distance between each interval on a scale is equivalent, from low interval to high interval. For example, the difference between 90 degrees Fahrenheit and 100 degrees Fahrenheit is the same as 110 degrees Fahrenheit and 120 degrees Fahrenheit.
In addition to having the same qualities as interval levels, ratio levels can have a value of zero. The cost difference between two pairs of shoes that are $10 and $20, respectively, is the same as the cost between two pairs that are $20 and $30. However, you won’t find shoes that cost less than $0.
Interval scale Vs Ratio scale: Points of difference
|Variable property||All variables measured in an interval scale can be added, subtracted, and multiplied. You cannot calculate a ratio between them.||Ratio scale has all the characteristics of an interval scale, in addition, to be able to calculate ratios. That is, you can leverage numbers on the scale against 0.|
|Absolute Point Zero||Zero-point in an interval scale is arbitrary. For example, the temperature can be below 0 degrees Celsius and into negative temperatures.||The ratio scale has an absolute zero or character of origin. Height and weight cannot be zero or below zero.|
|Calculation||Statistically, in an interval scale, the arithmetic mean is calculated.||Statistically, in a ratio scale, the geometric or harmonic mean is calculated.|
|Measurement||Interval scale can measure size and magnitude as multiple factors of a defined unit.||Ratio scale can measure size and magnitude as a factor of one defined unit in terms of another.|
|Example||A classic example of an interval scale is the temperature in Celsius. The difference in temperature between 50 degrees and 60 degrees is 10 degrees; this is the same difference between 70 degrees and 80 degrees.||Classic examples of a ratio scale are any variable that possesses an absolute zero characteristic, like age, weight, height, or sales figures.|