How can I be sure my girlfriend is 100% girl?

No. If salmonella is evenly distributed between brown and white eggs, a person eating only brown eggs exposes himself to precisely the same degree of risk as someone eating both, where they consume in the same quantity.

I didn't do the mathematics but I just assumed that figure was calculated from the 1.7% number. If you date only one of the genders, your chances of meeting an intersexual is down by half.

No it's not. Think about it, if you've halved the number of intersexual people but also halved the population (by excluding one gender) then the odds remain the same...

I didn't do the mathematics but I just assumed that figure was calculated from the 1.7% number. If you date only one of the genders, your chances of meeting an intersexual is down by half.

But if the 11.3% figure has already taken that into account then just forget that part.

It's not that intuitive unfortunately You need to take the odds of a person not being intersex (98.3%, or 0.983), raise it to the power of the number of people entered into a relationship with, and subtract the result from one. So if you date 60 people, the chances of at least one being intersex are 1 - (0.983^60), or 64.3% to one decimal place.

I admit maths is not my strongest subject in school but doesn't this mean it's even less likely than I thought?

I thought statistically after 60 people the possibility should be theoretically 100%. And now it's only 64.3%.

5 partners is much more reasonable than 10 (I think 6 is around the number the average person has sex with in their lifetime, not for long-term relationships), and yes 8% is not small. But still very unlikely. As I've said, normal people don't worry about their partner being secretly gay or HIV+ (both are more likely than this) so why worry about this?

I know there can be selection bias, but I'm saying we don't know anything about either of these people here. His selection bias could be caused by his previous personal experience or the news article posted instead of anything to do with this girl.

Think it through logically. If you draw four cards from a standard deck, is one guaranteed to be a spade simply because the odds are one in four? What you said before (that you'd expect 1 intersex person after dating 60) implies a greater than 50% chance after 60 (so that you'd be more likely to than not) - there is of course no such thing as total certainty, and in reality you exceed a 50% chance after 40 people, lower than your calculation

The offside rule (in football I assume) is pretty simple....

The offside rule (in football I assume) is pretty simple....

I actually didn't know about the rule until I just looked it up right now, I agree with you. I don't see how it's not simple ??? If I can understand it in <4 mins then it can't be that bad

I've always been fond of the thesis that it's more to do with men being bad at explaining it, rather than women bad at understanding

I'd say the stock markets and things like foreign exchange rates are further examples. They fluctuate over even with only remotely related rumours.

Mexicans being Mexicans would actually be a further support to my point - the average Mexican should have more exposure to violence than someone from most other countries, but they still freaked out over their very very first school shooting that happened at a atypical school that has a unique student body. I'd also say Britons rushing to get an EU passport in fear of needing a visa to travel in the future (very unlikely) is another example of that.

How many people heard the story about the intersex model? Now, how many people posted a question on a forum about their girlfriend possibly being intersex? I'm sure the latter is a small minority of the former. Even though it might be most likely that the reasoning for this person to ask this question is not based on 'reality' as such, that doesn't change the fact that this does increase probability of gf being intersex, because there is a chance that it is based on reality. I understand this is a little confusing (I'm not being patronising here).

I think the kind of panics you are talking about are real, but firstly, they aren't as big in term of percentage of population as you think (because of media only concentrating on the extremes, and it can take only small percentage of population suddenly changing behaviour to create big problems), and secondly, some people might decide they will get a passport or whatever but soon after change their mind, forget, put it off etc. Also, what's this intersex news story compared to the big events you are talking about, they are obviously more likely to spur the public to action.

Just some thoughts.