Warum brauchen wir Statistik? Ein Beispiel

Im Editorial der New York Times vom 17. März 2009 steht geschrieben:

Estimated HIV/AIDS prevalence among young adul...

Estimated HIV/Aids prevalence among young adults (15-49) by country in 2008.
Image via Wikipedia

"As reported on Tuesday by journalists who accompanied the pope on his flight to Africa, Benedict said that distribution of condoms would not resolve the AIDS problem but, on the contrary, would aggravate or increase it. The first half of his statement is clearly right. Condoms alone won’t stop the spread of H.I.V., the virus that causes AIDS. Campaigns to reduce the number of sexual partners, safer-sex practices and other programs are needed to bring the disease to heel.

But the second half of his statement is grievously wrong. There is no evidence that condom use is aggravating the epidemic and considerable evidence that condoms, though no panacea, can be helpful in many circumstances." (Zum Editorial)

Wie sieht nun es mit der letzten Aussage aus? Wie ist der aktuelle Stand des Wissens: Wird die HIV Inzidenz durch die Verwendung von Kondomen beeinflusst? Und falls ja, in welche Richtung?. Hierzu wurde ein systematischer Review der bekannten wissenschaftlichen Literatur im Rahmen der Cochrane Initiative durchgeführt. Das Ergebnis:

"This review indicates that consistent use of condoms results in 80% reduction in HIV incidence. Consistent use is defined as using a condom for all acts of penetrative vaginal intercourse. Because the studies used in this review did not report on the "correctness" of use, namely whether condoms were used correctly and perfectly for each and every act of intercourse, effectiveness and not efficacy is estimated. Also, this estimate refers in general to the male condom and not specifically to the latex condom, since studies also tended not to specify the type of condom that was used. Thus, condom effectiveness is similar to, although lower than, that for contraception." (Zum systematischen Review - Cochrane Library)

Die zweite Aussage des Papstes ist damit zumindest aus wissenschaftlicher Sicht so nicht haltbar. Hier wurde durch die systematische Zusammenfassung methodisch einwandfreier Studien gezeigt, dass die Verwendung von Kondomen die HIV Inzidenz deutlich verringert.Thanks to @laikas for the idea to use this as an example





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