Table I.

Summary of results from first study (simple main effects)

Measurement	Nationality and unrealistic optimism bias												F	P-value	ηp²
	Poland				Iran				Kazakhstan
	Myself		Student from my university		Myself		Student from my university		Myself		Student from my university
	M	SD	M	SD	M	SD	M	SD	M	SD	M	SD
Wave I
No match	5.42a	2.42	5.93a	2.23	5.06b	2.59	6.66b	2.49	3.04c	2.27	4.76c	2.64	41.53	< 0.001	0.05
Match	5.37a	2.04	5.89a	2.02	4.86b	2.29	6.35b	1.96	3.09c	2.51	5.25c	3.28	22.87	< 0.001	0.11
Wave II
No match	5.19a	2.55	5.71a	2.54	3.84b	2.23	5.86b	2.38	3.84c	2.23	4.79c	2.26	43.72	< 0.001	0.06
Match	5.19a	2.21	5.53a	2.03	4.93b	1.94	6.43b	1.76	2.73c	1.87	4.72c	2.24	30.36	< 0.001	0.14

^a,b,cPost-hoc significant differences with Bonferroni correction.