Use this criteria to segment your users according to their numeric user ID. This can be useful for things like A-B testing, where half of your users match the criteria and half do not. Use the <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/:nth-child" target="_blank">syntax for CSS :nth-child</a> for the expression, for example: <code>2n</code> for even numbers and <code>2n+1</code> for odd numbers.