Hi Stephen- Looks like a case of data-mining to me as well. Unless they show an apriori rationale for such a strange grouping then I would disregard their findings.
-Don. ----- Original Message ----- From: sbl...@ubishops.ca Date: Monday, December 7, 2009 8:11 am Subject: [tips] Birth order effects for cooperation? To: "Teaching in the Psychological Sciences (TIPS)" > OK, here's another study I'm mulling over. Courtiol et al (2009) > have just reported an experiment on cooperation in college > students as a function of birth order. Their measure of > cooperation is an objective one, taken from the results of a two- > person game. The game provides numerical values for trust and > reciprocity, determined by how much money each player sends > or returns to his partner. Although birth order studies are > infested with methodological problems, this design, as far as I > can see, successfully avoids them. > > The history of claims for birth order effects is not a happy one > (e.g. see Judith Rich Harris' "Four Essays on Birth Order" > (2004) at http://xchar.home.att.net/tna/birth-order/index.htm > and > also her more recent review in "No Two Alike" (2006)--the > chapter headed 'Birth Order and Other Environmental > Differences Within the Family"). So I paid attention when > Courtiol et al reported positive effects of birth order on both > trust > and reciprocity. > > But here's the catch. They provided a complex statistical > analysis (to me, anyway) but their analysis depends on a > curious grouping of birth order: first-borns comprised one > group, > and later-borns the other. But the later-born group also > included > only children (without siblings). On logical grounds, one would > think that only children belong in the first-born category > instead. > > Their justification for doing this was inspection of the data. > For > trust: "Means of x [their monetary datum] for middleborn, > lastborn and only children appeared much closer to each other > than to the mean of x for firstborns (Table 2); these three > categories were therefore pooled." For reciprocity: "Only > children and laterborns were pooled because their average > amounts sent (y) were closer to each other than to the average > amount sent by firstborns (Table 2)." > > My own inspection of their data suggests that without this post- > hoc categorization, they would not have been able to report > significant results. Is their move kosher, or do we have a case > of > data-massaging here? > > _Science_ has a news item on the study at > http://tinyurl.com/ylc4l34 > It does not mention the peculiar definition of "later-borns". > > Stephen > > Courtiol, A. Raymond, M. and Faurie, C. (2009). Birth order > affects behaviour in the investment game: Firstborns are less > trustful and reciprocate less. Animal Behaviour, 78, 1405-1411. > > ----------------------------------------------------------------- > Stephen L. Black, Ph.D. > Professor of Psychology, Emeritus > Bishop's University > e-mail: sbl...@ubishops.ca > 2600 College St. > Sherbrooke QC J1M 1Z7 > Canada > ----------------------------------------------------------------- > ------ > > --- > To make changes to your subscription contact: > > Bill Southerly (bsouthe...@frostburg.edu) > Don Allen, Retired Formerly with: Dept. of Psychology Langara College 100 W. 49th Ave. Vancouver, B.C. Canada V5Y 2Z6 Phone: 604-733-0039 --- To make changes to your subscription contact: Bill Southerly (bsouthe...@frostburg.edu)
