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SURVEY METHODOLOGIES

Interval Scale

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What is an Interval Scale?

An Interval scale is a quantitative measurement scale in the four “levels of measurement” as per S.S. Stevens’ classification. This scale is not only useful for ranking and ordering of attributes but also provides us with the degree of difference.

The interval scale measures its data along with the equal distance between two adjacent values. This is the reason behind its name “interval”. However, an interval scale cannot have zero as its value; zero has an arbitrary place in this scale but not a complete absence of variables.

For instance, for an IQ test, one may use an interval scale. The use of an interval scale can help measure that the difference between an IQ of 80 and 90 is the same as an IQ of 90 and 100. At the same time, the score cannot be zero, because the minimum level for IQ is 40.

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Characteristics of Interval scale

  • The interval scale is a numerical scale that not only contains data based on rank and order but also tells the difference between two variables and their value.
  • The scale may show the value as zero but it does not mean true zero or absence.
  • For example, in the case of temperature, the indication for zero degrees Fahrenheit and Celsius does not mean the absence of temperature. The value is used to describe the phenomena where equal parts of ice, water, and salt freeze.
  • Interval scale can comprise the whole as well as the fractional number as its data variables.
  • Interval scale cannot measure the ratio between two values. The data between two values cannot be multiplied or divided.
  • With the data of an interval scale you can only learn about the order and difference but not about proportion.
  • Interval scale can support a statistical or data analysis and thus, is a preferred measurement scale in statistics or scientific analysis.
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How to measure Interval data?

  • Variables of an interval scale can be analyzed with mode, median and arithmetic mean to find the central tendency.
  • To specify the variability you need to compile from the data the range, standard deviation, and variance.
  • While both parametric and non-parametric tests are possible for interval data, using parametric tests can lead to a stronger conclusion.

Some parametric tests used for interval data are as follows.

  • T-test: The aim is to compare the means of the variables. It requires 2 samples.
    • For example, it can help determine the difference between scores of two different schools.
  • ANOVA: The aim is again for the comparison of means of the data. It requires a minimum of 3 samples.
    • For example, it can help calculate the difference in the average score of a trainee from three tests.
  • Pearson’s r: The aim of this test is to assess the correlation between the attributes of the data. It requires 2 variables from data.
  • Simple linear regression: The aim of this process is to determine regression. It requires 2 variables.
    • For example, if you want to generate a survey to analyze the relationship between income and happiness, you can use this procedure to find if there is a linear relationship between the two.

After understanding what an Interval scale is how it works let’s look for ways to use the scale.

Examples of Interval scale

The interval scale generally uses questionnaires to collect data. To receive feedback from your target audience the choice of the option must be properly generated. This will help assign a numerical value to the data which will make the difference between two variables equal and easy to measure.

Means to use Interval scale

  • Likert Scale: A five-point or seven-point Likert-type question can help receive audience feedback. You can use any kind of Likert scale to determine the value, by denoting each attribute with a number.

For example, on an agree-disagree scale you can allot numbers as following:

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  • NPS or Net Promoter Score: A Net Promoter Score comes with a scale of 1 to 10 and can prove to be a good idea to evaluate employee, customer, student, or client satisfaction. Rating from 1 to 10 in increasing order of satisfaction can be a simple and clear method to use an interval scale.
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When to use interval scale

  • For measuring Temperature but only in degree of Fahrenheit or Celsius one may use an interval scale.
  • Competitive exams can use the interval scale procedure for their purpose.
  • The interval scale can serve for survey purposes by the collection of the age range. Age is a numerical variable as well as measurable.
  • If you want to find out how much time a group of people spend every day on American series, you can use an interval scale to figure out not only the amount of time but also the difference in time spent by each individual.

 You may have come across interval scales, maybe online or in reality, where you were a part of the target audience. Now you can curate your own interval scale to collect data.

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