Hur påverkar stamning ett barns prestationer i skolan? I en ny, fyndigt betitlad studie, ”The Kid’s Speech: The Effect of Stuttering on Human Capital Acquisition”, börjar författarna med att beskriva tidigare forskning:
There is a large body of work showing that speech impairments are associated with sharply lower scores on tests of reading and math (Catts 1993; Walker et al. 1994; Stothard et al. 1998; Catts et al. 2002; Knox 2002; Nathan et al. 2004; Catts et al. 2008; Harrison et al. 2009; Eide and Showalter 2010; Law et al. 2010). There is also evidence, albeit weaker, that children with speech impairments go on to receive fewer years of education than their counterparts without speech impairments (Snowling et al. 2001; Johnson et al. 2010). The results of these studies could indicate that speech impairments
lead, in a causal sense, to reduced academic performance and educational attainment. However, most studies in this area have used non-representative samples, and, to our knowledge, none have attempted to account for the potential influence of unobservables. Thus, there exists the possibility that their results were driven by difficult-to-measure factors at the level of the community, family or individual.
Som tur är försöker denna studie ta sådana faktorer i beaktande för att utröna om stamningen kan sägas ha kausal effekt på skolprestationer. Följande resultat erhålls:
Our baseline ordinary least squares (OLS) estimates are consistent with the findings of previous studies: respondents who reported having a problem with stuttering tend to have lower grades than their counterparts who did not report a problem with stuttering. Stuttering is also associated with a lower probability of graduating high school and a lower probability of attending college. However, when we restrict our sample to full biological siblings (including twins) and add family fixed effects, these associations become much smaller in magnitude, suggesting that family-level unobservables play an important role. Moreover, when we control for a history of ADHD or the presence of another learning disability, the estimated effects of stuttering shrink dramatically and become statistically indistinguishable from zero at conventional levels. These findings suggest that the impact of stuttering on human capital acquisition is much weaker than previously argued.
Måhända kan dessa resultat lugna föräldrar till stammande barn, i alla fall över själva stamningen.