Results and discussion In table 1.5 below, the p-values of the Wilcoxon rank-sum test are shown for the two time points of measurement of overestimation. Although overestimation does not differ between the treatment and control before the quiz, respondents do feel more confident about their own score after the quiz in the treatment group than in the control group (p-value 0.09*). The median in the treatment group is 0, while the median of the control group is -1. This means that respondents feel more confident about their own performance in the treatment group, but not necessarily overconfident. Interesting is that respondents in the control group were slightly overestimating their own score before the quiz, but after the quiz they underestimated their own score (Friedman’s test, p-value 0.003**). There is even a significant negative change in overconfidence in the control group, while such a significant change did not occur in the treatment group. On the other hand, in both groups overestimation has decreased over the two time points of measurements looking at the means of overestimation in table 1.7 in Appendix 1. The Wilcoxon signed-rank test shows that respondents are significantly less overconfident in their own scores after the quiz in the control and treatment group, p-values are 0.035** and 0.004**, respectively. The medians of the treatment group are not indicating this result. By looking at the means (before: 1.03 & after 0.03) there is indeed less overconfidence after the quiz in the treatment group. In conclusion, respondents who are surrounded by lower-skilled workers suffer more from overestimation, suggesting that group composition has an impact on people’s Also, the general level of overestimation dropped after they answered the quiz questions. But only in the control group is this change significant. Treatment group: median Control group: median P-values: Wilcoxon rank sum test Before the quiz 0 1 0.6 After the quiz 0 -1 0.09* P-values: Wilcoxon signed-rank test 0.035** 0.004** P-values: Friedman’s test 0.221 0.003** *P-value is significant at 10% significance level. Table 1.5 **P-value is significant at 5% significance level.
Table 1.2 Summary statistics on samples of students Treatment group (n=30): students participate in quiz with low skilled and other participants Control group (n=30): students participate in quiz with other participants that are students as well Age (years, mean) 24.2 22.1 Male (nr. of students) 20 9 Female (nr. of students) 10 21 Bachelor (nr. of students) 13 22 Master (nr. of students) 17 8 Phd (nr of students) 0 0 Average number of siblings 1.6 1.8 Happiness grade (0-10) 7.5 7.3 Table 1.3 Test of normality: Shapiro-Wilk test Dependent variables P-values overestimation before the quiz 0.014** over-placement before the quiz 0.015** over-precision before the quiz 0.005** overestimation after the quiz 0.376 over-placement after the quiz 0.000** Over-precision after the quiz 0.000** **P-value is significant at 5% significance level. Table 1.6 Descriptive statistics of the dependent variable overestimation before and after the quiz Descriptive statistics overestimation Treatment group Control group Mean before 1.03 0.268 Mean after 0.03 -0.83 Median before 0 1 Median after 0 -1 Minimum & Maximum before -2 & 8 -4 & 3