Is it statistically more likely for girls or guys to get into audition groups, such as plays, musicals, showchoirs, etc?
There are many many more girls than boys interested in theatre majors. Statistically, therefore, it’s more likely for a boy.
Something I heard a long time ago (but have no verifiable proof) is that 75% of rolls in existing plays and musicals or written for men, and 25% of auditioners are male. So yes, odds are better - BUT that does not mean to say that men have it easy making it as a professional performer. They absolutely do not. But it is statistically more likely