To Spank, Or Not to Spank?

"Three recent, widely reported studies on spanking children claimed to show that the disciplinary practice impairs cognitive development in children. Together, they held out the promise of providing the latest, definitive word on a passionate debate. ... Effects can be attributed to the wrong cause, statisticians say: rather than spanking causing problems in children, it is possible that their exisiting cognitive problems can make spanking more likely. Moreover, any effects of spanking are difficult to measure and probably small. ... Spanking studies have a long history of fueling rather than settling the corporal punishment question. Earlier findings that spanking can contribute to aggressive behavior in children helped spur the American Academy of Pediatrics to study the issue and recommend against spanking in 1998--a conclusion that is still disputed. ... Den Trumbell, vice president of the [American College of Pediatricians], says studies need to distinguish between appropriate spanking--following a warning and done in privacy following specific, proscribed misbehavior--and reactive, anger-based spanking. 'Spanking gets a bad name of late, because parents tend to use it when having a bad day,' Dr. Trumbull said", my emphasis, Carl Bialik at the WSJ, 14 October 2009, link: http://online.wsj.com/article/SB125548136491383915.html.

Which caused what? These spanking studies look so weak they could have been done by economists or criminologists.