Sibling spacing and intellectual development: A closer look at the confluence models.

Abstract

Zajonc and his coauthors have presented three confluence models that attempt to explain variations in intellectual development by the size and spacing of an individual's sibship and, most recently, by the age of the individual at testing. A closer look at two of these models revealed several major problems of internal consistency and external correspondence to data. The use of the child spacing variable in both models was particularly suspect. In addition, the most recent confluence model appears to have little applicability to within-families data due to the model's inability to account for individual differences in intellectual growth functions among siblings. The past use of between-families data for substantiating within-families models is also discussed. Finally, new between-and within-families data showed essentially no relationship between sibling spacing and intellectual development.

The Effects of Family Structure on the Educational Attainment of Siblings in Hungary

“…The intellectual family climate, which does not even take into account parental IQ, is considered to be so important that the model can dispose of these other factors. Until now, it has seemed impossible to replicate the initial results obtained with the confluence model (Brackbill and Nichols, 1982;Galbraith, 1982;Steelman, 1985;Retherford and Sewell, 1991). Moreover, since the assumptions underlying the confluence model seem unrealistic, and since it claims to be applicable to intelligence only, which is something quite different from educational attainment, we will not go into it in any further detail.…”

“…Empirical results on spacing have often yielded no effect at all (Schooler, 1972;Cicirelli, 1978;Steelman, 1985). However, if anything, results suggest that wide spacing is beneficial for children's life-chances (Galbraith, 1982), and again the reasons for this have typically been thought to be associated with economic resources. 2 These results refer to the United States, where financial resources do indeed seem to affect educational attainment.…”

Educational attainment of 25year old Norwegians according to birth order and gender

“…Studies that address withinfamily effects have been published in the past (e.g., Galbraith, 1982;Hauser & Sewell, 1985;Record, McKeown, & Edwards, 1969;Retherford & Sewell, 1991), but the literature was dominated by between-family designs. More recently, several studies with within-family designs have been published.…”

“…Also, instrumental variables approaches have been applied (Black et al, 2005;Conley & Glauber 2006). Study outcomes have been both intellectual test scores Galbraith, 1982;Guo & VanWey, 1999a,b;Record et al, 1969;Retherford & Sewell, Intelligence 38 (2010) 123-136 1991;Rodgers et al, 2000;Wichman et al, 2006) and educational attainment (Black et al, 2005;Kalimijn & Kraaykamp, 2005;Kantarevic & Mechoulan, 2006).…”

The Tale Retold: A Response to Zajonc

“…Although Zajonc dismisses my work as unworthy of serious scholarly attention, I am certainly not the lone voice in the wilderness (Gailbraith, 1982;Grotevant, Scarr, & Weinberg, 1977;Hauser & Sewell, 1985;Olneck and Bills, 1979;Rodgers, 1984). Zajonc's reaction, although raising some interesting points, fails to change the evidence.…”