Nominal number
A nominal number, also known as a categorical number, is a numeral employed solely for the purpose of labeling, identifying, or naming entities without conveying any inherent quantitative value, order, or mathematical significance.[1] In statistical contexts, nominal numbers form the basis of the nominal scale of measurement, the most basic level where data categories are distinguished but not ranked or arithmetically manipulated.[2] Unlike cardinal numbers, which denote exact quantities (e.g., "five apples"), or ordinal numbers, which indicate sequence or rank (e.g., "second place"), nominal numbers serve purely identificatory functions and do not support operations like addition or comparison of magnitude.[3] Common examples of nominal numbers include telephone area codes, postal ZIP codes, social security numbers, and sports jersey numbers, where the numerals act as unique identifiers rather than measures of amount or position.[4] In everyday applications, such numbers appear in contexts like product serial numbers and license plates, emphasizing categorization over numerical properties.[5] This usage underscores their role in organizing information efficiently without implying relational values between the labels. The concept of nominal numbers is fundamental in fields such as statistics, data science, and mathematics education, where distinguishing measurement scales helps determine appropriate analytical methods—nominal data, for instance, is typically analyzed using frequency counts or chi-square tests rather than means or correlations.[2]Fundamentals
Definition
A nominal number is a numeral or sequence used solely for naming, labeling, or identifying entities without implying any quantity, order, or magnitude. In this context, the numbers function as arbitrary symbols or codes, devoid of mathematical operations such as addition, subtraction, multiplication, or comparison for greater/lesser value. This concept aligns with the nominal scale in measurement theory, where numerals serve only as labels or type numbers with no quantitative significance, permitting only determinations of equality or difference.[6] Key characteristics of nominal numbers include their lack of arithmetic meaning and their role as arbitrary assignments, such as tags or identifiers, that do not represent inherent values or hierarchies. Unlike quantitative numbers, they cannot be meaningfully manipulated through standard numerical processes, emphasizing their purpose as non-measurable descriptors. These properties ensure that nominal numbers prioritize identification over any evaluative or calculative function.[6] The term "nominal" derives from the Latin nominalis, meaning "pertaining to a name," from nomen ("name"), underscoring its function as something existing in name only rather than possessing substantive numerical value. Nominal numbers can consist of purely numeric digits or alphanumeric combinations, with no intrinsic worth beyond their identificatory role. This etymological root highlights the symbolic nature of such numbers across linguistic and statistical applications.[7]Historical context
The practice of using numbers as labels for identification, rather than for counting quantities or establishing order, predates the 20th century and appears informally in historical records, though without a theoretical framework distinguishing it from quantitative or ordinal roles. A more systematic conceptualization emerged in statistics during the early 20th century, with psychologist Stanley Smith Stevens providing the foundational formalization. In his seminal 1946 paper, Stevens outlined four scales of measurement—nominal, ordinal, interval, and ratio—positioning the nominal scale as the most basic, where observations are assigned to categories based solely on equality or difference, without implications of order or magnitude. This classification addressed the need to analyze qualitative data in psychological and scientific research, marking nominal numbers as tools for grouping rather than measuring. Key milestones include Stevens' 1946 framework, which influenced interdisciplinary adoption in statistics and related fields.Classifications and Distinctions
Relation to cardinal and ordinal numbers
Cardinal numbers represent quantities and are used for counting discrete objects, such as "three apples," where arithmetic operations like addition and subtraction can be meaningfully applied to determine totals or differences.[8] In contrast, nominal numbers function solely as labels or identifiers, such as a jersey number "99," and do not convey any sense of quantity, precluding the application of arithmetic operations.[9] Ordinal numbers denote position or rank within a sequence, for example, "first place" in a race, establishing an order among elements but without assuming equal intervals between positions.[10] Unlike ordinal numbers, nominal numbers impose no such ordering, treating each label as discrete and incomparable in terms of sequence or hierarchy.[8] The distinctions among these number types can be summarized as follows:| Aspect | Nominal Numbers | Cardinal Numbers | Ordinal Numbers |
|---|---|---|---|
| Primary Purpose | Identification and labeling | Counting and quantifying amounts | Ranking and indicating position |
| Mathematical Operations | None (only set-theoretic mappings) | Full arithmetic (addition, subtraction, etc.) | Ordering and comparisons (e.g., greater than) |
| Example | ZIP code 90210 | Five books | Third in line |