So you agree that this study and others conducted in the same manner are fundamentally flawed, but you still say it demonstrates something valuable. Bullshi|t says I. Either a study is reliable or it's not. Using a poorly constructed soapbox to stand on when you make your point doesn't give your argument more authority, it just means you'll use anything to get your point across. Bear in mind that I agree with your position on corporal punishment.

The IQ scores of children ages two to four who were spanked were 5 points lower four years later than children who were not spanked.
The IQ scores of children ages five to nine who were spanked were 2.8 points lower four years later than children who were not spanked.

psychologist Elizabeth Thompson Gershoff, PhD, of the National Center for Children in Poverty at Columbia University
Duke University
University of Missouri-Columbia,
University of South Carolina,
Columbia University
Harvard University
University of North Carolina at Chapel Hill
National Institute of Mental Health
American Psychological Association

All of these institutions have reputations for outstanding, peer reviewed, rigorous scientific investigative work.

If we were talking about A single study that showed there are negative aspects to spanking, yeah, I would take IT with a grain of salt. However, there have been so many studies on this topic and they all come to essentially the same conclusion...spanking carries far more negatives than positives....can you find even a single study that would support the "spanking is no big deal, I was spanked and I turned out ok" argument?

Sure you may well have turned out ok (I was spanked and I did) but how much better would I have been if my parents had not opted to use fear and threats to manipulate me into compliance (which btw didn't work anyway in my case...I'm a stubborn woman). The thing is that none of us knows how different we would be if we hadn't been spanked so to make the argument that you turned out ok is weak...turned out ok compared to what? You will never know.

It has only been very recently that many studies have shown that if there is a good parent many kids do better after the divorce than would have been the case if mom and dad stayed together because the level of conflict in the home is, well, absent.

Another big surprise – divorce harms children
Thursday, January 22, 2009
By Robert Franklin

Here’s a shocker.  Divorce harms kids.  The latest evidence is reported here (The Australian, 12/8/08).
It reports on an international study detailed in the Journal Comparative Sociology. The study looked at educational outcomes for over 30,000 Australians and found that children lose up to a year of school incident to divorce. The study concludes,
"Divorce's impact on children's education is, we suggest, in a large part a consequence of the disruption, the loss of parental control and the difficulties that a sole parent or a step-parent faces in raising children - all of which reduces children's prospects for success in school."
This is just the latest evidence we have to support the notion that our 30 + -year experiment with no-fault divorce has failed. For decades, the concept of no-fault divorce was vigorously promoted by, among others, the National Association of Women Lawyers. The theory was that adults shouldn’t be trapped in a relationship that benefitted neither party. Into the bargain, the no-fault divorce crowd told us that children would be better off too if they weren’t exposed to constantly bickering parents. By 1983, every state but two had adopted no-fault divorce laws and, to no one’s surprise, the divorce rate soared.
Throughout the 1970s and early 80s, the divorce rate increased reaching over 40%. But now, thanks mostly to people’s actual experiences as well as the small avalanche of studies like the one reported on by The Australian, divorce rates are declining.
No-fault divorce laws should be modified, but more important is public education about the harmful effects of divorce on children. They are many and varied. Children suffer from divorce and when children suffer, society suffers too.? 
http://mensnewsdaily.com/glennsacks/2009/01/22/another-big-surprise-%E2%80%93-divorce-harms-children/

I don't disagree with that comment but there is also something that needs to be taken into consideration when one looks at psychological studies in particular. Most study something that is fairly narrow and many studies are designed to control for certain variables. When one looks at the discussion and conclusion section of the studies, the researchers will list the problems inherent with the design, the size of the sample, the things that were controlled for. With the divorce studies, for example, there have been at least twenty years or more of studies that did not even look at parenting style and efficacy, they were only looking at the age of the children at the time of divorce, whether the non-custodial parent was involved, etc. it has only been very recently that they have been factoring parenting into the studies. Many studies even failed to consider how the child was doing before the divorce, when mom and dad were bringing them up in a turbulent home, to see if the academic and social behaviors had deteriorated or if they were merely doing less well than their peers in good nuclear families, which would have been the case divorce or not. It has only been very recently that many studies have shown that if there is a good parent many kids do better after the divorce than would have been the case if mom and dad stayed together because the level of conflict in the home is, well, absent.

So it is not that any single study is massively flawed but psychological studies tend to feed off each other. We have findings from a study, there will be others done with larger samples, etc. to see if the results can be replicated. Then they start looking at the holes in the studies, so they design new studies to account for those and it may take 20 or more years to really get to the point that they have actually been able to isolate the one factor, in this case spanking, to gauge exactly what is going on.

The study that was originally cited in the OP illustrated that the IQ gap closed from the younger children to the older children so just using simple logic it is highly likely that those children that were five points behind at 4 and 5 years old were not quite so behind later suggesting that the children were not perhaps raised in an intellectually stimulating environment and that being in school where they were challenged properly made a difference in the IQ.

Psychological studies are frustrating from this standpoint because you really need a huge volume for the results to be empirical

and many people that read them, report on them, or quote them, don't read the whole study and information gleaned from an article, as has been mentioned by several posters, is really suspect because they often don't understand what they are writing about and cherry pick what they report, like leaving out the disclaimers by the researchers relative to problems in design, variables not accounted for, etc., because they want the best bang for the buck with the article. Shock value stuff sells papers and magazines.

Spanking creates defiant, aggressive children

By Jared Wadley
News Service
Spanking makes it more likely, not less, that children will be defiant and aggressive. And physical punishment puts kids at risk for increased mental health problems, anti-social behavior and serious injuries, a new U-M report shows.
"There is little research evidence that physical punishment improves children's behaviors in the long term," says Elizabeth Gershoff, the report's author and an associate professor in the School of Social Work.
The report, released in collaboration with the Phoenix Children's Hospital in Arizona, offers a review of empirical research on the effects physical punishment has on children.
Gershoff analyzed 100 years of research and published studies on physical punishment, spanking in particular. Most findings indicate that spanking is an ineffective parenting practice within the United States and around the world.
"There is growing momentum among other countries to enact legal bans on all forms of physical punishment," says Gershoff, whose research focuses on the impacts of parenting and violence exposure on child and youth development over time.
The practice is regarded as a violation of international human-rights law, she says.
Several recent studies reveal that many parents still physically abuse their children, especially children ages 1 and 2. By the time children reach fifth grade, 80 percent have received physical punishment.
In multiple studies, spanking has been found to lead to mental health problems in children, such as anxiety and depression, alcohol and drug use, and poor psychological adjustments. These problems also increase stress levels, she says.
Gershoff's report indicates that spanking can also harm parent-child relationships. If a child avoids painful experiences, and if he or she sees the parent as the source of pain from corporal punishment, he or she may avoid parents. This can interfere with a child developing trust and closeness, she says.
So how should parents discipline their children? Gershoff says children behave better when they are motivated by praise or the promise of rewards rather than by threats of punishment. Children need teaching and guidance from parents so they can learn how to make better choices in the future.
"(Spanking) does not teach children why their behavior was wrong or what they should do instead," the report states.
The findings appear in "The Report on Physical Punishment in the United States," www.phoenixchildrens.com/about/community-outreach-education/
effective-discipline.html.
http://www.ur.umich.edu/0809/Mar30_09/07.php

as i stated before.. i was spanked and i am not defiant nor aggressive. I am depressed.. but that is due to a different set of circumstances that occured in my late teens and not related to spanking. It is not a violation of human rights as the act doesn't actually damage the child and they do learn the bounderies..well..cos.. my entire family are living proof.. we are all intelligent and successful and we were all spanked and it was worse for my parents ad grand parents as tyhey used to recieve the cain across the palms of their hands.

aslong as you are not physcially beating the child and it is done in an controlled, non emotional manner with an open handed gentle slap that doesn't leave a mark.. then all is good.

CORPORAL PUNISHMENT: Towards Constructive Child Discipline
Report
During the Commission on Human Rights, UNESCO launched a new report entitled "Eliminating Corporal Punishment - The Way Forward to Constructive Child Discipline". The United Nations Committee on the Rights of the Child has consistently recommended States Parties to the Convention on the Rights of the Child to prohibit corporal punishment and other forms of violence against children in institutions, in schools, and in the homes. The past 25 years have shown that the elimination of corporal punishment is not easy to achieve.
To discipline or punish through physical harm is clearly a violation of the most basic of human rights. Research on corporal punishment has found it to be counterproductive and relatively ineffective, as well as dangerous and harmful to physical, psychological and social well being. While many States have developed child protection laws and systems violence still continues to be inflicted upon children.
This UNESCO publication provides a comprehensive approach, including the main steps to be considered in the process of eliminating corporal punishment, and provides tools to accomplish this goal. It shows the human rights imperative and describes several aspects of the negative consequences and implications that are caused. It details practical steps for more constructive and effective child discipline practices, and ongoing supports for long-term change.
An international panel of experts presents descriptions of some of the constructive discipline orientations and practices known to be applied in Asia, Africa, Europe, the Middle East, and South America. They include: involving learners and their parents in decisions about codes of conduct and associated practices; providing guidance in the selection of positive models in peers and classmates; family meetings and inter-generational dialogue; rendering services to the community to rectify rule infractions; and exploring ethical-moral meanings and implications in current events. Additionally, two experts on Indigenous peoples provide descriptions of constructive child rearing and discipline orientations and related practices for peoples they know well.
For more information, contact:?UNESCO ?7 Place de Fontenoy, 75352 Paris 07 SP, France?Tel: + 33 1 45 680 686; Fax: + 33 1 45 685 626?Website: www.unesco.org

Sure you may well have turned out ok (I was spanked and I did) but how much better would I have been if my parents had not opted to use fear and threats to manipulate me into compliance

The thing is that none of us knows how different we would be if we hadn't been spanked so to make the argument that you turned out ok is weak

can you find even a single study that would support the "spanking is no big deal, I was spanked and I turned out ok" argument?

Any halfway decent study controls for variables like making sure the study isn't overlooking things like the intellectual stimulation in the environment, etc.

Um, I'm not sure which apples to buy my kids for thier lunches... I guess I should find a study to tell me what apples to buy, cause god knows, if it's a study it MUST be right.

And now it's illegal to spank your kids

That Guy, during childhood until about 25, we are learning and developing, at times at a lightening fast pace. Our physical bodies mature. We develop both emotionally and intellectually.

Children need discipline in the form of teaching and allowing them to basically do what they want/when they want is in my opinion just a different form of abuse.

Does this change your mind about spanking your child?

What about the fear and threat of being put into your room or another room for hours at a time, or having your favorite most treasured toy taken away for days or being told that you could never do -(insert your favorite activity here)- anymore? Do you not think that to certain kids that would have a traumatic impact on thier lives and cause a drop in IQ? Just because a parent doesn't spank thier kids, doesn't mean that there aren't other non-physical disciplines that may cause an IQ drop.

No they don't, because it is impossible to initially isolate for everything. It may be impossible to ever isolate the single variable because we don't live in labs.

Listen, it is obvious why so many of you are trying to refute a hundred years of research findings. It is because most of you have either spanked your children on occasion, or spank your children regularly, and you don't want to think you have done anything to harm your children.

However, just because the negative effects aren't obvious, it doesn't mean they aren't there.