A lot of our friends and relatives recently (less than 4 months) had babies or are currently expecting.  As of today 6 babies were born and 5 were boys and 1 girl.  Of 13 people who are expecting 8 are boy, 2 girl and 3 are unknown.

It seems that this is against the normal 50/50 odds of having boy/girl.  In this group there are (or will be) 13 boys 3 girls and 3 are unknown.   There seems to be a lot of boys.  I saw something like this once before about 15 years ago where there were 23 babies born all with 12 months and 19 were girls and 4 were boys.

I guess occasionally sexes are determined in bunches.

Anybody else notice this?
 

Independent events.

There are different rates of conception versus birth.  Either females are more likely to be conceived, but males are more likely to survive to birth, or vice-versa.  The pH of the vagina has a lot to do with the survival of sperm, and a harsher environment leads to more of the stronger sperm sex (whichever one it is) surviving and thus more likely to impregnate.

The odds though are more 50/50 when looking at the entire population, I doubt it would be as accurate if looking at a small subset of related people.  If the vaginal secretions of the womenfolk have a tendency to be more acidic than the population as a whole, then those women would be more likely to give birth to either male or female babies, whichever is strongest.

I'm not sure of the specifics, it's been a while and I'm not going to bother looking up which one is more likely to survive a harsh vagina.

statistics of small samples

I HATE math word problems.