You survey many many school children and ask each one:
Do you have more brothers than sisters? or more sisters than brothers? or the same number?
Then you separate the boys’s answers from the girls’s answers
Which of the following is true?
- The answers from boys will be tilted toward having MORE sisters and LESS brothers
- The answers from boys will be tilted toward having MORE brothers and LESS sisters
- There will be no (statistically significant) difference.
The reason for answer 1 is: Since the ratio of boys/girls is 50/50, and you don’t count yourself in the answer, boys will tend to have more sisters and girls will tend to have more brothers
The reason for answer 2 is: Some families are uneven and have more boys. In these families you will see more boys having more brothers than sisters and less girls having more brothers than sisters. Some families are uneven and have more girls. In these families you will see more girls having more sisters than brothers and less boys having more sisters than brothers.
I thank Oded Margalit for this question given to me as a birthday gift.