PHP Checkbox can not show checked on edit page

There is a problem to show checked in checkbox on edit page. There is my code below:

SSC<input type="checkbox"  name="ssc"class="form-control" value="SSC"

<?php if(isset($ssc)) echo ($data[6] == 'SSC') ? 'checked':''; ?>/>

HSC<input type="checkbox"  name="hsc" class="form-control" value="HSC"

<?php if(isset($hsc)) echo ($data[6] == 'HSC') ? 'checked':''; ?>/>