Please help me correct a summary of my thesis

Hello,

I have to write a summary of my thesis in English. It's in psychology, but I'm mostly concerned about basic grammar and/or some formal language issues. Could someone check if the text below is correct?

The thesis was created to show relationships between bilingualism, understood in terms of Bialystok (2001), creative thinking from Popek (2000) and ability to understand metaphors presented by Kurcz (2011). The questionnaire included a question that was the basis of the first bilingual criterion, the Picture Metaphor and Written Metaphor from The Right Hemisphere Language Battery RHLB-PL by Karen Bryan in the Polish adaptation of Emilia Lojek (2007) and the Creative Behavior Questionnaire KANH-I Stanislaw Popek (2000). The study group consisted of second and third grade students in high school in both, French-speaking classes and Polish-speaking classes. The study involved 203 students: There were 66 correctly completed questionnaires in bilingual classes and 133 in the remaining classes.

The first criterion for bilingualism was self-evaluation of language proficiency, the second was attending French-speaking classes. Between such groups, the result of the Mann–Whitney U test was statistically significant only for the difference in the level of creative thinking between French-speaking classes and Polish-speaking classes (p=0.012, U=3449, d=-0.3369), which confirmed the theoretical assumptions. No difference in the ability to understand metaphors may be the result of selecting too easy questions. There is no difference in creative attitudes between persons who consider themselves bilingual and those who don’t . This may be the result of poor self-evaluation. The division into bilinguals and monolinguals should be based on more precise and objective criterion.