# Entropy

Checks whether the *entropy* value of a column matches
a given expression. Entropy measures the level of information that's contained in a message.
Given the probability distribution over values in a column, entropy describes how many bits
are required to identify a value.

**Syntax**

`Entropy`

`<COL_NAME>`

`<EXPRESSION>`

**COL_NAME**– The name of the column that you want to evaluate the data quality rule against.**Supported column types**: Any column type**EXPRESSION**– An expression to run against the rule type response in order to produce a Boolean value. For more information, see Expressions.

**Example: Column entropy**

The following example rule checks that the column named `Feedback`

has an
entropy value greater than one.

`Entropy "Star_Rating" > 1 Entropy "First_Name" > 1 where "Customer_ID < 10"`

**Sample dynamic rules**

`Entropy "colA" < max(last(10))`

`Entropy "colA" between min(last(10)) and max(last(10))`