**Core Concept**
Ordinal scales are a type of measurement scale used in statistics and research to express the relative magnitude or order of a variable. In ordinal scales, the data is ranked or ordered, but the differences between consecutive values are not necessarily equal.

**Why the Correct Answer is Right**
Ordinal scales are used when the data can be ranked or ordered, but the exact differences between consecutive values are not known. For example, in medical research, pain levels are often measured on an ordinal scale, where patients are asked to rate their pain as mild, moderate, or severe. This scale allows for the ranking of patients by their pain levels, but the exact differences between mild, moderate, and severe pain are not quantifiable.

**Why Each Wrong Option is Incorrect**
**Option A:** Interval scales are incorrect because they require equal differences between consecutive values, which is not the case in ordinal scales.
**Option B:** Nominal scales are incorrect because they are used for categorical data, where the data is not ranked or ordered.
**Option C:** Ratio scales are incorrect because they require a true zero point and equal differences between consecutive values, which is not the case in ordinal scales.

**Clinical Pearl / High-Yield Fact**
Ordinal scales are commonly used in medical research to measure subjective experiences, such as pain levels, quality of life, or patient satisfaction.

**Correct Answer: B. Nominal scales are incorrect because they are used for categorical data, where the data is not ranked or ordered.