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Interval scale vs Ratio scale

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The interval scale is third in the four “levels of measurement” while a ratio scale is the fourth and highest in order. There are but few differences between an interval scale and a ratio scale. To understand these differences let’s first understand their definition.

The interval scale collects and measures data where intervals between two points are of equal distance. The scale provides a degree of difference along with the rank and order of the values as collected from a market research or survey. An interval scale, however, has a zero point with an arbitrary presence. This means that the value of zero has no real meaning.

The ratio scale, on the other hand, has the characteristics of all the levels of measurement as created by S.S. Stevens. It can rank and categorize the data obtained through the scale. Moreover, the distance between two variables in a ratio scale is also equal in distance. In addition, a ratio scale has a true zero point, meaning the value of zero is not arbitrary.

To understand the difference between the two scales with the help of the definition, we can take the example of temperature.

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Interval Scale

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The point of degrees in both these scales has equal intervals of exactly one degree. For instance, the distance between 29 and 30 degrees is the same as the distance between 99 and 100 degrees.

However, due to the absence of absolute zero, you cannot tell by how much the temperature is higher or lower. For example, you cannot say if 40 degrees is twice hot as 20 degrees or if – 20 degrees is half as cold as -40 degrees.

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Ratio Scale

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Along with all the other values, in a Kelvin scale, the zero point has a relevant meaning. For instance, you can tell on a Kelvin scale that 40K is twice hot as 20K.

Also, the presence of absolute zero in a Kelvin scale means that nothing can be colder than OK. This is because on a ratio scale there can be no negative number.

Now let’s look into some other differences between interval and ratio scale.

Some parametric tests used for interval data are as follows.

  1. Variable
    • In an interval scale, the data collected can be added, subtracted, and multiplied. The scale allows computing the degree of difference but not the ratio between them.
    • A ratio scale permits not only addition, subtraction, and multiplication but also division. That is, you can calculate the ratio of the values.
  2. Calculation
    • In the case of an interval scale, to find out the central tendency, mode, median, and arithmetic mean is allowed. Statistical dispersion permits range and standard deviation. The coefficient of variation is not permitted because interval scale cannot define ratio.
    • On a ratio scale, you may use geometric and harmonic mean along with mode, and median to figure out central tendency. Also, range and coefficient of variation are permitted for measuring statistical dispersion.
    • On a ratio scale, the division between two units is meaningful. Whereas in an interval scale they do not hold any meaning.
  3. Magnitude
    • In an interval scale with the available data size can be measured and the magnitude of the variable as the multiple factors of a defined unit.The case of ratio scale is so that the magnitude as a multiple is a factor of one defied unit in terms of another.
  4. Zero
    • An interval scale can have negative values because the zero point does not mean an absence of value. Zero degrees Celsius does not mean the absence of temperature.
    • On a ratio scale, there are no negative values. The zero in a ratio scale means a total absence of variables.
    • For example, if you are conducting a survey to find out the number of work experience the newcomers in your office have. In this case, if someone answers with zero it means that they have no prior work experience.

Examples of interval and ratio scale

  • Time and duration are two examples of interval and ratio scale respectively.
    • Time is the value of the interval scale because there is no zero. You cannot tell when time started.
    • Duration is a case of ratio scale for the fact that duration has a starting point. The zero in duration has a meaningful presence. You can tell that 20 days is twice of 10 days.
  • A ratio scale can measure any data that has “zero points” characteristics. A ratio scale is ideal for measuring age, weight, height, etc. In marketing research it can calculate sales, shares, the volume of the customer, etc.
  • An interval scale is mostly used to gather feedback based on agreement, satisfaction level, or likelihood. It is commonly found in question-type surveys where the choice of options are so scaled that a numerical value can be allotted to them, in order to calculate.

The interval and ratio scale both have quantitative variables and are of higher level in the four levels of measurement. However, there are certain differences that set them apart.

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