**Coefficient** is synonymous with **number, factor or proportion**. **Etymologically**, it is composed of the Latin prefix *cum*, which means ‘with’, and *efficients*, which derives from the verb of *efficere*, and translates ‘do’, ‘act’. Therefore, in certain contexts, it functions as an adjective that refers to something that, together with something else, contributes to producing a certain effect.

In **Mathematics**, for example, **coefficient is a multiplicative factor** , that is, the constant number to the left of a variable or unknown variable and multiplies it. For example, 3X = X + X + X, where 3 is the **coefficient** of the variable X.

In **Physics**, the **coefficient** is a **numerical value** that indicates the degree or intensity of a certain property or characteristic, be it of a body or a phenomenon.

Within **Psychology**, **coefficient** can also refer to a measurement of a person’s reasoning skills to calculate their intellectual level (see here IQ ).

## Coefficient of variation

In **Statistics**, the **coefficient of variation** is a measurement used to analyze the relationship between the standard deviation of a sample and its arithmetic mean, all in order to find the relative dispersion. In this sense, the **coefficient of variation** is a way of expressing the variability of the data, leaving out the influence of the order of the dimensions in the variable, but considering the proportion between the means and the standard deviation.

## Correlation coefficient

The **Pearson correlation coefficient** (named after Karl Pearson, who formulated it) is a measure used in **Statistics** to calculate the degree of linear relationship between two random variables, so it is also known as the **linear correlation coefficient**.

## Coefficient of friction

In **Physics**, the **coefficient of friction**, also called the **coefficient of friction**, indicates the opposition to sliding offered by the surfaces of two bodies in contact. In this sense, there are two types of friction coefficients: the static one, that is, the one with two resting surfaces, where no movement is registered, and the dynamic one, which is when both surfaces are in relative motion, the one with respect to the other. Generally the coefficient of friction is expressed with the Greek letter μ.

## Expansivity

As a **coefficient of expansion**, in **Physics**, the quotient obtained from the measurement of the relative change in length or volume that a body undergoes, whether it is in a solid, liquid or gaseous state, when it is subjected to a temperature change is called , which may be ascending or descending. In this sense, the temperature increase will be proportional to the expansion, be it linear, superficial or volumetric.

### Linear expansion coefficient

The **linear expansion coefficient** measures the variations in the size of the solid bodies (be it width, length or height of the body, never more than one) when they are subjected to temperature changes.

### Coefficient of surface expansion

The **coefficient of surface expansion** is also found on solid surfaces, which expand or contract according to the variation in temperature, and is recorded in two dimensions. In this sense, this type of expansion coefficient varies the total surface area, as it occurs in two dimensions.

### Volumetric expansion coefficient

The **volumetric expansion coefficient** is used to calculate the variations in volume (that is, in three dimensions) that occur on solid, gaseous or liquid surfaces, when changes in temperature cause the body to contract or dilate.