Nelson uses selection bias in column
Issue date: 4/22/05 Section: Editorial/Opinion
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04/22/05 - To the Cigar,
Let's clarify a few points in relation to Mr. Nelson's comments about moral decay, homosexuality and AIDS, starting with the medical facts.
One part of the confusion relates to the distinction between the "cause" of a disorder versus its "transmission" from one person to another. The HIV virus is the cause of AIDS. The disease is typically transmitted by IV drug use, blood transfusions or sexual contact, either heterosexual or homosexual.
Another piece of the confusion over the facts stems from lack of clarity about what population is being discussed and whether the statistics pertain to all cases of AIDS or only to newly reported cases in a given year.
Worldwide, the most common mode of HIV transmission, by a wide margin, is heterosexual activity. There are far more cases of HIV infection in Africa than anywhere else in the world and in Africa most new cases develop from heterosexual contact.
In the United States, homosexual activity was the leading method of transmission of the virus until recently. Intravenous drug use is presently the leading mode of transmission (for new cases in the U.S.) but that method will soon be overtaken by heterosexual transmission.
Since homosexual activity was the leading basis of transmission of HIV in the U.S. for several years, the majority of all presently existing cases began in that way, but obviously that will change as more and more new cases develop from intravenous drug use and heterosexual activity.
Mr. Nelson's original statement on the issue (a) confused cause with mode of transmission, (b) cited out-of-date statistics, and (c) was unclear about what population of people (worldwide or U.S. only) he was discussing.
Those weaknesses in his argument do not establish bigotry, but only a weak understanding of the medical issues. What does suggest bias in Mr. Nelson's views is his selection of one particular "fact" from a myriad of statistics about AIDS to imply fallaciously that medical support exists for his views, which are, in fact, rooted solely in his personal system of moral judgments.
Let's clarify a few points in relation to Mr. Nelson's comments about moral decay, homosexuality and AIDS, starting with the medical facts.
One part of the confusion relates to the distinction between the "cause" of a disorder versus its "transmission" from one person to another. The HIV virus is the cause of AIDS. The disease is typically transmitted by IV drug use, blood transfusions or sexual contact, either heterosexual or homosexual.
Another piece of the confusion over the facts stems from lack of clarity about what population is being discussed and whether the statistics pertain to all cases of AIDS or only to newly reported cases in a given year.
Worldwide, the most common mode of HIV transmission, by a wide margin, is heterosexual activity. There are far more cases of HIV infection in Africa than anywhere else in the world and in Africa most new cases develop from heterosexual contact.
In the United States, homosexual activity was the leading method of transmission of the virus until recently. Intravenous drug use is presently the leading mode of transmission (for new cases in the U.S.) but that method will soon be overtaken by heterosexual transmission.
Since homosexual activity was the leading basis of transmission of HIV in the U.S. for several years, the majority of all presently existing cases began in that way, but obviously that will change as more and more new cases develop from intravenous drug use and heterosexual activity.
Mr. Nelson's original statement on the issue (a) confused cause with mode of transmission, (b) cited out-of-date statistics, and (c) was unclear about what population of people (worldwide or U.S. only) he was discussing.
Those weaknesses in his argument do not establish bigotry, but only a weak understanding of the medical issues. What does suggest bias in Mr. Nelson's views is his selection of one particular "fact" from a myriad of statistics about AIDS to imply fallaciously that medical support exists for his views, which are, in fact, rooted solely in his personal system of moral judgments.
