## ::Relative change and difference

### ::concepts

In any quantitative science, the terms **relative change** and **relative difference** are used to compare two quantities while taking into account the "sizes" of the things being compared. The comparison is expressed as a ratio and is a unitless number. By multiplying these ratios by 100 they can be expressed as percentages so the terms **percentage change**, **percent(age) difference**, or **relative percentage difference** are also commonly used. The distinction between "change" and "difference" depends on whether or not one of the quantities being compared is considered a *standard* or *reference* or *starting* value. When this occurs, the term *relative change* (with respect to the reference value) is used and otherwise the term *relative difference* is preferred. Relative difference is often used as a quantitative indicator of quality assurance and quality control for repeated measurements where the outcomes are expected to be the same. A special case of percent change (relative change expressed as a percentage) called *percent error* occurs in measuring situations where the reference value is the accepted or actual value (perhaps theoretically determined) and the value being compared to it is experimentally determined (by measurement).

**Relative change and difference sections**

Intro Definitions Formulae Percent error Percentage change Other change units Examples See also Notes References External links

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Change::value Relative::absolute ''x''::values ''y''::costs Which::error Percent::example

In any quantitative science, the terms **relative change** and **relative difference** are used to compare two quantities while taking into account the "sizes" of the things being compared. The comparison is expressed as a ratio and is a unitless number. By multiplying these ratios by 100 they can be expressed as percentages so the terms **percentage change**, **percent(age) difference**, or **relative percentage difference** are also commonly used. The distinction between "change" and "difference" depends on whether or not one of the quantities being compared is considered a *standard* or *reference* or *starting* value. When this occurs, the term *relative change* (with respect to the reference value) is used and otherwise the term *relative difference* is preferred. Relative difference is often used as a quantitative indicator of quality assurance and quality control for repeated measurements where the outcomes are expected to be the same. A special case of percent change (relative change expressed as a percentage) called *percent error* occurs in measuring situations where the reference value is the accepted or actual value (perhaps theoretically determined) and the value being compared to it is experimentally determined (by measurement).

**Relative change and difference sections**

Intro Definitions Formulae Percent error Percentage change Other change units Examples See also Notes References External links

PREVIOUS: Intro | NEXT: Definitions |

<< | >> |