A measurement scale refers to the system or method used to assign numbers or labels to variables or attributes in a study. These scales help researchers measure, compare, and analyze data accurately. The choice of measurement scale determines the type of statistical tools that can be applied.
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There are four major types of measurement scales arranged from the simplest to the most complex level of measurement:
- Nominal Scale
- Ordinal Scale
- Interval Scale
- Ratio Scale
1. Nominal Scale
A nominal scale is the simplest measurement scale that categorizes data using numbers/letters for identification and classification.
- Numbers or labels used in this scale are only for identification or classification and do not carry numerical meaning.
Examples include gender (male/female), marital status (single/married), blood group (A, B, O), or assigning numbers to players in sports. Since the data only represent categories, statistical operations like average cannot be applied.
2. Ordinal Scale
An ordinal scale categorizes data with a meaningful order or ranking, but the difference between the ranks is not measurable.
- It shows the relative position of items but not how much greater one is than another.
Examples include education levels (primary, secondary, bachelor, master), customer satisfaction ratings (satisfied, neutral, dissatisfied), or ranking students by performance. Although the data indicate order, mathematical operations like addition or subtraction cannot be applied.
3. Interval Scale
An interval scale measures data with equal intervals between values, but it does not have a true zero point. Because the intervals are consistent, mathematical operations such as addition and subtraction are possible.
- However, ratios (like “twice as much”) cannot be interpreted due to the lack of an absolute zero.
Common examples include temperature measured in Celsius or Fahrenheit, and calendar years. For instance, the difference between 20°C and 30°C is the same as between 30°C and 40°C.
4. Ratio Scale
A ratio scale is the highest and most precise level of measurement that has all the properties of interval scale, plus a true zero point, which allows full mathematical and statistical operations.
- With a true zero, it is possible to say one value is “twice” or “three times” another.
Examples include height, weight, age, income, number of students, and length. For example, a weight of 60 kg is twice as heavy as 30 kg because zero weight means “no weight.”