samlet årgang - Økonomisk Institut - Københavns Universitet

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NATIONALØKONOMISK TIDSSKRIFT 2005. NR. 3
is the students’ age when admitted. The ’error’ is a stochastic error term assumed to
follow a normal distribution with zero mean and a constant variance.
The interpretation of the model is as follows:
– The expected grade of a student who has been admitted via quota-1 is:
0 + 5 *AGEADMIT,
i.e. the intercept of the model plus the coefficient of »ageadmit« times the age of the
student at the time of the admission. If this age is 20.3 years, we have: 0 + 5 *20.3.
– Similarly, the expected grade of a non-Scandinavian quota-2 student is:
0 + 1 + 2 *GPA + 3 *MOTAVR + 5 *AGEADMIT
For example, if the student has a GPA = 8.46 (the average), has MOTAVR = 12.80
(the average) and is 23.78 years old when admitted, we have: 0 + 1 + 2 *8.46
+ 3 *12.80 + 5 *23.78.
– The expected grade of a Scandinavian quota-2 student is:
0 + 1 + 2 *GPA + 3 *MOTAVR + 4 + 5 *AGEADMIT
For example, if the student has GPA = 8.87 (the average), has MOTAVR = 12.80 and
is 23.7 years old when admitted, we have: 0 + 1 + 2 *8.87 + 3 *12.8 + 4
+ 5 *23.7
4. The results
The results are presented in the following two tables; table 1 for the first year courses
and table 2 for the second year courses. 17 Note that the tables present a parsimonious
model for each course. The »-« indicate the variables that are omitted compared to equation
(1) due to acceptance of the null hypothesis that the coefficients of these variables
were simultaneously zero (F-test results are reported in the final rows of the tables). 18
Two misspecification tests are performed: the White’s general test for heteroscedasticity
and the Jarque-Bera (JB) test for normality of the error term. In both cases
a p-value smaller than 0.05 would indicate that the model was mis-specified. As can
be seen, this is not the case.
Our model has some explanatory value for all but two courses, viz. Intercultural
Communication (123) and International Business Law (241). For these two courses
none of the variables (that we examined) have an effect on grades. In these two courses,
the expected average grade is 9.17 and 8.66, respectively. For all other courses the
17. Instead of running regressions for each course (which reduces the number of observations available), we
could have run one pooled regression that includes a dummy for each course. This would have increased the
number of observations and presumably reduced the standard deviations and improved the fit. We decided,
however, not to follow this procedure as that will remove the valuable information that one gets from running
individual regressions – as will be discussed below, some variables work for some courses but not for
others. Running one regression would blur that picture.
18. For completeness we report the estimation results of the full models based on equation (1) in appendix 2.