Soc Psychiat Epidemiol (2010) 45:639–646 Table 2 Multilevel regression analyses on internalising and externalising problem behaviour 643 Fixed part predictor Intercept Ethnic minority status Proportion minority students Minority status 9 proportion Class atmosphere Female Age Educational level Family afﬂuence Class size Random part Variance intercept Variance class level Slope variance minority status Covariance Deviance Internalising problem behaviour Externalising problem behaviour Model 1 Model 2 Model 1 Model 2 Model 3 4.728 (1.936)* 0.521 (0.412) 0.711 (0.848) 3.968 (0.241)*** 0.239 (0.109)* -0.336 (0.072)*** -1.328 (0.188)*** 0.017 (0.038) 62.163 (1.365) 1.363 (0.505) 3.176 (2.883) 0.671 (1.011) 31837.828 4.634 (1.939)* 0.895 (0.596) 1.281 (1.078) -1.377 (1.596) 3.973 (0.241)*** 0.238 (0.109)* -0.334 (0.072)*** -1.340 (0.189)*** 0.020 (0.038) 62.171 (1.365) 1.359 (0.503) 2.946 (2.855) 0.724 (1.010) 31837.090 1.213 (1.814) 1.002 (0.420)** -0.119 (0.843) -0.682 (0.219)** 0.710 (0.102)*** -0.380 (0.068)*** 0.132 (0.171) 0.086 (0.036)* 50.556 (1.120) 1.391 (0.438) 8.841 (3.486) 0.439 (0.948) 30962.180 1.064 (1.809) 1.915 (0.601)** 0.983 (0.994) -3.469 (1.641)* -0.673 (0.219)** 0.707 (0.101)*** -0.376 (0.068)*** 0.111 (0.121) 0.089 (0.036)** 50.602 (1.121) 1.358 (0.432) 7.803 (3.352) 0.503 (0.920) 30957.814 7.588 (1.881)** 1.872 (0.583)** 0.648 (0.988) -3.163 (1.584)* -1.479 (0.153)*** -0.655 (0.216)** 0.624 (0.099)*** -0.350 (0.066)*** 0.198 (0.170) 0.091 (0.035)** 49.675 (1.102) 1.243 (0.417) 7.093 (3.142) -0.193 (0.890) 30795.266 Coefﬁcients are unstandardized. Standard errors are reported between parentheses * P \ 0.05, ** P \ 0.01, *** P \ 0.001 Dutch majority students Ethnic minority students individual level and the proportion of ethnic minorities at the class level (v2(1) = 4.366, P = 0.04). Since the func- tion of ethnic density may not automatically be assumed to be linear, a quadratic term was added to the model. How- ever, this did not signiﬁcantly improve the model ﬁt (v2(1) = 0.857, P = 0.178). Examining the interaction effect, as displayed in Fig. 1, we ﬁnd that as minority students constitute a smaller proportion in class, on average they report a higher level of externalising problem behav- iour. As the proportion increases, their level of problem behaviour draws closer to that of the Dutch majority stu- dents, with equal levels reached when approximately two- third of the class is of foreign, non-Western descent. The level of problem behaviour of Dutch majority students is not related to the ethnic composition of the class. Hence, an increase in the number of minority students in class does not lead to higher levels of problem behaviour among the majority students. In sum, the analysis revealed that as the proportion of ethnic minority students in a given class increases, the level of externalising but not of internalising problem behaviour of minority students decreases. With respect to the explained variance, we ﬁnd that the regres- sion model of externalising problem behaviour including the interaction effect has an R2 of 0.39, indicating that almost 40% of the variance at the class level is explained by this model. 16 15 r iou14 v a eh13 b m le12 b o r gp11 n i z lia10 n r e tx 9 E 8 7 0 0,2 0,4 0,6 0,8 Proportion minority students in class 1 Fig. 1 The effect of class ethnic composition on Dutch majority and ethnic minority students’ externalising problem behaviour Discussion In this study the ‘ethnic density hypothesis’ is conﬁrmed with respect to externalising problem behaviour among 123