

More Sex is Safer Sex (1996) - dmoney
http://slate.msn.com/?id=2033

======
nostrademons
There're some questionable assumptions in this paper, notably this one:

"What we really want is to minimize the number of infections resulting from
any given number of sexual encounters; the flip side of this observation is
that it is desirable to maximize the number of (consensual) sexual encounters
leading up to any given number of infections."

He's saying that there's this ratio, infections per sexual encounter, that
they want to minimize. And the easiest way to minimize this is to increase the
denominator. If you have a universe with a skewed (self-selected)
distribution, then as you add more people to a category, you'll increasingly
get more marginal people. In this case, it's people who have fewer sexual
partners and hence are less likely to carry AIDS, resulting in a reduced
chance of infection.

Whether this is the metric you care about is debatable. If you're a public
health official, you probably care about the absolute _number_ of infections,
not the number per sexual encounter, and so this only helps if it brings the
probability low enough that the disease can't sustain itself.

Similarly, if you're a married guy who just wants a faithful and devoted wife
and kids, you don't care about the chance of infection per sexual encounter,
you care about the absolute chance of infection within your life time. This is
minimized by not having sex with anyone, or, failing that, having sex with
someone who only has sex with you.

Only people who regularly have sex with lots of partners would benefit from
this - for them, the metric is chance of infection per sexual encounter (since
they'll be having lots of sexual encounters anyway), so why shouldn't they?

~~~
lkozma
"If you're a public health official, you probably care about the absolute
number of infections, not the number per sexual encounter"

Perhaps they made the assumption that the total number of sexual encounters
over the entire population is roughly constant. With this assumption the
distinction would not matter.

~~~
ringm
They're arguing for "increased sexual activity by conservatives" which
obviously means they're arguing for increase in total number of sexual
encounters over the entire population.

~~~
lkozma
No, they argue that this would lead to less demand for prostitutes, which
would balance it out.

In effect they say that disease would spread more slowly in a graph with less
highly connected hubs and more balanced number of connections per node. This
is quite unsurprising.

~~~
ringm
Sure, this is quite obvious though I did not understand how they could balance
out the increase, so I did not even mention this option.

The point about prostitutes was just a thought experiment, and it looks rather
far from reality. The second thought experiment about Joan hooking up with
Maxwell seems much more realistic, but I don't see why Maxwell wouldn't hook
up with someone else the same day. Actually, the more promiscuous side usually
takes the initiative, so I'd say it is quite likely that if not for Joan, some
other poor girl would get AIDS anyway.

------
stretchwithme
HIV infections per encounter will go down if you have a lot of sex, this is
true.

And it will to zero forever once you get infected.

But its the likelihood of infection overall that I am concerned with. The more
sex you have, the likelier it is that you will have an infective encounter
earlier.

the fact remains that if people never have sex, they will never get infected.
If they only have sex with one person in their life, and that person follows
the same rule, no one will be infected either.

But that's not reality. so we should follow some simple rules, which can be
found at <http://evensafersex.com>

------
araneae
Although tfa is slim on details, it seems that the economist is assuming that
the total number of sexual encounters per unit time is constant, and that
increasing the activity of some people would only change the distribution in
the number of sexual contacts.

Fair enough-- if you could change the distribution, that would probably slow
down the epidemic. But, counter intuitively, it would also increase the number
ultimately infected.

This is something network-theorists have spent a lot of time on. See for
example:
[http://rspb.royalsocietypublishing.org/content/274/1628/2925...](http://rspb.royalsocietypublishing.org/content/274/1628/2925.full)

~~~
lotharbot
The article made the mistake of analyzing only a tiny piece of the system and
attempting to draw conclusions for the whole system.

One of the mistakes the article makes is in the statement that, if
"conservative" girls went out twice as often, the chances of an HIV transfer
are decreased because the guy has twice as many potential partners who are
HIV-negative. What's missing is the recognition that, if the guy is already
HIV positive, he now has twice as many potential partners who he can pass the
infection on to.

The changed network could either slow down _or_ speed up the spread of HIV,
depending on various specific details (how many men have HIV, how many women
have HIV, how many connections to non-carriers do the men have vs the women,
and so on.)

As you correctly note, even if this particular change slows down the rate of
infection in the present, it may ultimately increase the total number of
infections. It may even slow the infection rate for a few years and then
suddenly speed it up as some particular critical threshold is reached.

------
nkassis
This article sounds a lot like Russian roulette. Increasing the number of
chambers making it safer to play. It's not clear to me that the virus would
just die out. I'll probably end up talking out of my hat but with graph of all
the connections (sexual encounters). Would it not be possible to show that
you'd need a very connected graph where most people have a small number of
encounters and that almost everyone sticks to a low number. One hyper
connected infected person (or multitple), could end up infecting a large part
of the graph. I would assume that if he affects a large enough number of
people, they (before discovering their infection) could infect their
connection and ... snowball. In their model, they seem to say that even if
their are very promiscuous people, getting non promiscuous people to get more
connected would improve the odds. I don't see how that would reduce the number
of infected people and kill the virus.

Like I said, I have no clue if this is correct or complete crap, never done
anything related to disease and how they spread.

~~~
lkozma
I think what the article argues is exactly this: there would be less hyper-
connected nodes if the nodes would be more locally connected. The spreading of
the disease would happen much more slowly in this case. This fits in with the
theory of scale-free networks.

links:

<http://en.wikipedia.org/wiki/Small-world_networks>

<http://en.wikipedia.org/wiki/Degrees_of_separation>

<http://en.wikipedia.org/wiki/Watts_and_Strogatz_model>

[http://en.wikipedia.org/wiki/Erd%C5%91s%E2%80%93R%C3%A9nyi_m...](http://en.wikipedia.org/wiki/Erd%C5%91s%E2%80%93R%C3%A9nyi_model)

~~~
nkassis
I think I understand that now. Although, not sure that people who are very
promiscuous would enjoy having more competition ;0)

Thanks for the links, this article made me want to go back and look into this
stuff more. Relevant to my current work also.

~~~
lkozma
Also, if you want a more readable and entertaining introduction, I highly
recommend the book "Linked: The new science of networks" by Barabasi.

------
cduan
Two questions come to mind:

1\. It would be pretty simple to write a computer simulation to test this, no?
Would anyone care to do so?

2\. I don't know enough about the AIDS situation in Africa to say whether it
is empirical evidence for or against this paper. Is anyone else more familiar
with this?

~~~
philwelch
"1. It would be pretty simple to write a computer simulation to test this, no?
Would anyone care to do so?"

I'm on it. Results in a later reply.

~~~
philwelch
Preliminary results: holding sex drive and promiscuity constant, decreasing
societal shyness (i.e. making single people more likely to go out and meet
someone to fuck) seems to increase population infection rates rather than
decreasing them. This is true if shyness is independent from promiscuity. (My
simulation tends to send more promiscuous people out to meet someone to fuck
more often by increasing their partner-switching rate, so shyness is indeed
independent.)

Don't just take my word for it, run my code:
<http://github.com/philwelch/SexSim>

If anyone's interested, let me know and I can work up a blog post and improve
my code. (Also, if my code is wrong, let me know or send me a patch.)

EDIT: I have a bug which may invalidate my results. Stand by for fix.

EDIT 2: No, results still valid. Possible fix pushed.

~~~
Natsu
I took game theory back in college. I noticed something wrong about that
article: a complete lack of math. It's not that I don't believe there are
counter-intuitive things that can happen. But I sure don't believe them
without proof.

And your simulation is a lot more interesting than anything found in that
article.

~~~
philwelch
It was a fun exercise. It was great for remembering a handful of things about
statistics and experiment design--for instance, it was impossible to get good
results until I started doing controlled runs on the same randomly generated
population rather than regenerating, because the effect of changing social
shyness (while there) is way, way smaller than the effect of the random
variations in promiscuity and sex drive.

I may want to play with adding condoms to the simulation, though. My
transmission rate is based upon the HIV transmission rate for unprotected anal
sex, which is pretty clearly an upper bound--that's why especially slutty or
outgoing populations get >50% infection rates after 20 years seeding from 1%
infection rate. You also see the odd run where you just have a 1% infection
rate after 20 years--probably cases where the randomly seeded HIV+ individual
is especially shy and has a low sex drive.

Also, it would have been a lot more interesting if I could have generated
random values along different distributions, or...well, lots of things would
have helped.

------
lkozma
©1996 Microsoft Corporation (?)

~~~
drawkbox
Article from Slate magazine which they used to own before The Washington Post
bought it in 2004.

------
jrockway
Incidentally, any problems with my sex life are likely not due to unsubsidized
condoms.

------
kingkilr
It's a pretty good book too (I enjoyed all of Landsman's books).

------
jonpaul
Articles like this are what we should find on Digg. I don't want to be that
snooty bastard, even though I am.... I'm not sure how this is relevant to
Hacker News? However, I'm impressed by the mature comments. Can we not turn
into Digg?

~~~
cianestro
It seems a lot of people are concerned about HN turning into other
communities. How is this avoidable? Require everyone to debug a snippet of
code before registering or logging in? I personally wouldn't mind this.

~~~
ComputerGuru
Don't worry about it and it's all good. HN is self-balancing. I've been here
for 884 days according to my profile, and I've _always_ been hearing these
worries since day 1. Somehow, thankfully, HN works. It has not turned into
Reddit, Digg, or MySpace regardless of what people say. Yes, it has changed
over time, no it's not a worse place.

~~~
cianestro
Yeah, kind of thought so--a little diversity can be refreshing imo. I noticed
that HN redirects you to a previous submission if you use the same url.
Perhaps the same could be done if you post something with the same url used on
a previous reddit or digg submission.

------
sscheper
This is Hacker News. As long as masturbation doesn't cause aids, all is good.

~~~
ComputerGuru
It's clearly a hacker question. There's math, simulation, and girls involved.
A true hacker can turn interesting articles like this into very hacker-ish
engineering puzzles - read the other comments and see what I mean.

------
seles
pointless article it can be summarized in two sentences

assumption: woman don't want to have sex, men do.

conclusion: it is better for men if women are more promiscuous.

~~~
gjm11
Your summary has nothing to do with the actual content of the article.

