scientists evidence

I have recently been on a very interesting site called impactlab which has reported their findings on a scientific investigation in the USA, which states how children who are spanked have lower IQs than children who are disciplined in other ways. What really amuses me is how can anybody be shocked by these findings? I'm certainly not surprised as i feel that children who are spanked regularly are taking a beating to their self esteem which has an affect on their emotional well being. If a child's emotional development is affected in this way then, of course, it will have a knock on effect on all other areas of development especially their cognitive development.