Guest Posted January 20, 2002 Report Share Posted January 20, 2002 Oh boy, all my formulas got messed up! But it seems that all of you are already advanced students of statistics, because I can't find one false calculation in this thread Link to comment Share on other sites More sharing options...
Guest Posted January 20, 2002 Report Share Posted January 20, 2002 curiousguy, I'm convinced you're a mathematical genius and I know for sure I'm a mathematical buffalo, so I'm just going ????????????????????????????????????????????? I'm impressed, even if your formulas got messed up. I would have thought it's the formula for a nuclear-powered spaceship. Link to comment Share on other sites More sharing options...
Guest Posted January 20, 2002 Report Share Posted January 20, 2002 Post deleted by DoxyBlue Link to comment Share on other sites More sharing options...
Guest Posted January 20, 2002 Report Share Posted January 20, 2002 Db_sed_aloha, you would see that your formula is the same as mine, if only mine wouldn't have got messed up. Just remember that P in your formula is the probability of getting infected AT LEAST one time: if you are interested in the formula for the probability of getting infected x times, you should use the more general formula (and this time written in your formula style): P(x)=(i!/((i-x)!x!))(r exp x)((1-r)exp(i-x)). Link to comment Share on other sites More sharing options...
Guest Posted January 20, 2002 Report Share Posted January 20, 2002 I will give an example: if transmission rate of HIV-transmission through peno-vaginal sex is 1 in 2000 or 0.0005 (0.05%) on average and, let's say 10% of all prostitutes is HIV-infected in Bangkok/Pattaya/Phuket, then the probability of HIV-infection per sexual contact with a prostitute in these areas = 0.00005. Then the formula indicates that, if you have 300 unprotected sexual encounters with such women, the probability of zero HIV-infections is 98.51%, of one HIV-infection is 1.48% and more than one infection is 0.01%. Thus only a small probability. Of course the formula gets really interesting when talking about curable STD's and/or greater transmission rates. Let's look at a male who has a (small, almost invisible) genital ulcer, caused by mechanical damage or infection by micro-organisms like herpes simplex virus or haemophilus ducreyi (chancroid). These kind of damages and/or infections are common in the world, especially in tropical Third World countries. Yet the probability of HIV-transmission is easily increased 100-fold by these damages, so the probability rate of infection per contact in these (common) cases has increased to 0.005, still assuming 1 out of 10 sex workers is HIV-positive. Then the formulas of binomial distribution tell us: the probability of getting zero infections of the HIV-virus after 300 unprotected sexual contacts is only 22.23%, the probability of getting one infection of the HIV-virus after 300 unprotected sexual contacts is 33.51%, the probability of getting two times infected by the HIV-virus after 300 unprotected sexual contacts is 25.18%, the probability of getting three times infected by the HIV-virus after 300 unprotected sexual contacts is 12.57%, and so on. The same kind of risks goes for herpes simplex, hepatitis B and syphilis. The probability rates for chlamydia, gonorrhoea and genital warts are even higher. Link to comment Share on other sites More sharing options...
Sukhumvit Posted January 20, 2002 Report Share Posted January 20, 2002 The plural of formula is formulae. A small point but relevant when people are disseminating statistical information. Link to comment Share on other sites More sharing options...
Guest Posted January 20, 2002 Report Share Posted January 20, 2002 Thank you, Sukhumvit, for your correction. I am very glad this is the only mistake I've made that you have found untill now, because actually English is not my mother language so I would not be surprised if I make many more mistakes when I try to write English... Actually, I have always been quite weak on the English language, I think am better on Spanish, German, French and Dutch... Link to comment Share on other sites More sharing options...
Sukhumvit Posted January 20, 2002 Report Share Posted January 20, 2002 curiousguy au contraire I didn't scan your post for mistakes but the point which I'm sure you got was that science/statistics is/are all about precision. Hence, where there are basic mistakes in language then one should consider whether there are also mistakes in the science. Anyway, I see that you don't speak Welsh, Manx or Cornish. You're not so smart now are you. Link to comment Share on other sites More sharing options...
rickfarang Posted January 21, 2002 Report Share Posted January 21, 2002 All this discussion of statistics is ineresting, but let's all keep in mind that when something happens to you, its not longer an issue of probablility. Two things you can do ("...short of abstinence", as was said): Get tested so you know, and minimize future risk. Also, that one statistic - vaginal sex being 10 times as risky as oral. There are very, very few documented cases of oral transmission of HIV. This sounds more like a guess or an expression of a feeling than a statistic based on actual data. Rick Link to comment Share on other sites More sharing options...
Guest Posted January 21, 2002 Report Share Posted January 21, 2002 Originally posted by Rick Farang: "There are very, very few documented cases of oral transmission of HIV." True, though logic tells me that if you have ulcers in your mouth or bleeding gums and there's some menstrual blood - bingo! Due to several "unlucky" circumstances the odds will rise considerably. One problem is that if the statistics say the odds are one in a million and you're a bit of a worry-wart or hypochondriac, you will be convinced that you'll be the unlucky bastard, the one in a million, who'll draw the ticket. Even one in a million is one too many in my book. Link to comment Share on other sites More sharing options...
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