How to resize image in item selector xml

How to resize item of selector in xml

<?xml version="1.0" encoding="utf-8"?>
<selector  xmlns:android="http://ift.tt/nIICcg">
    <item android:state_checked="false" android:drawable="@drawable/check_box_2" />
    <item android:state_checked="true" android:drawable="@drawable/check_box_1" />
    <item android:drawable="@drawable/check_box_2" /> <!-- default state -->
</selector>