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Research Article

Oxytocin Increases Generosity in Humans

  • Paul J. Zak mail,

    To whom correspondence should be addressed. E-mail: paul.zak@cgu.edu

    Affiliations: Center for Neuroeconomics Studies and Department of Economics, Claremont Graduate University, Claremont, California, United States of America, Department of Neurology, Loma Linda University Medical Center, Loma Linda, California, United States of America

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  • Angela A. Stanton,

    Affiliation: Argyros School of Business & Economics, Chapman University, Orange, California, United States of America

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  • Sheila Ahmadi

    Affiliation: Division of Endocrinology, Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America

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  • Published: November 07, 2007
  • DOI: 10.1371/journal.pone.0001128

Reader Comments (6)

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Random allocation?

Posted by vonelm on 12 Nov 2007 at 17:50 GMT

A total of 68 males participated in the experiment with 34 of them receiving OT and 34 receiving placebo
http://plosone.org/article/info:doi/10.1371/journal.pone.0001128#article1.body1.sec4.p1

It is not clear whether this was an experiment with random allocation of participants to the study groups. If it was not, how did the investigators decide who should receive OT or placebo? And how did they ensure that both groups are comparable with regard to other possibly unmeasured factors?


RE: Random allocation?

astanton replied to vonelm on 13 Nov 2007 at 22:08 GMT

Participants were randomly allocated; this was a double-blind study, in which we did not know who was in the OT treatment and who was in the placebo treatment group. As for comparing the two groups for unintended (unmeasured) factors, we used dummies for several demographic variables: age, sex, number of friends, ethnicity, etc. We found no factors significant other than the treatment.


RE: RE: Random allocation?

vonelm replied to astanton on 19 Nov 2007 at 19:23 GMT

Thanks for clarification. I think it would have been helpful to use the terms "randomly allocated" and "double-blind" also in the abstract. Otherwise, the study is unlikely to be identified and indexed as a randomized trial.


RE: RE: RE: Random allocation?

astanton replied to vonelm on 22 Nov 2007 at 00:34 GMT

Thanks for your comment; it surely would have been a good idea... in the next paper we will watch out for this.


RE: RE: RE: RE: Random allocation?

bcreasy replied to astanton on 25 Apr 2008 at 05:13 GMT

I wonder if it's not too late to adjust it?


RE: Random allocation?

pzak replied to vonelm on 22 Nov 2007 at 15:14 GMT

Hi, we did randomly assign participants to groups. All ppts filled out more than 200 questions on social, demographic, and psychological factors. There are no substantial diff. between groups.