The cohort: “The Phase III clinical trial followed 2,499 HIV-negative men and transgender women (who had once been men) who have sex with men. The individuals, aged 18 to 67, lived in cities in one of six countries (Brazil, Ecuador, Peru, South Africa, Thailand and the U.S.) and were randomized to either the antiretroviral group, which took once-daily doses of Truvada (emtricitabine and tenofovir disoproxil fumarate, or FTC-TDF) or the placebo-pill group.”
An article recently published in Scientific American on preventative dosing of anti-retrovirals announces: "For HIV-negative men who have sex with men, taking preemptive antiretrovirals seems to reduce the risk of getting infected by about 44 percent, according to a new international study. Among those who reported having unprotected receptive anal sex, the prophylactic drug treatment was about 58 percent effective in preventing infection, and among all study subjects who took the recommended daily dose at least 90 percent of the time, the treatment had about a 73 percent efficacy in preventing transmission."      I am not an MD, and I don't know the medicine as well as I'd like, but the information is very poorly presented—dangerously so.      It's an example of how scientists can unwittingly make way for the promotion of bigotry.      The distinction “HIV-negative men" isn't significant other than as the most convenient group. Homosexual males were the first to begin reporting symptoms of Acquired Immune Deficiency Syndrome, and so make the best candidates for a longitudinal analysis. 
 For scientists, it can be chalked up to the problem of anachronism.      Elliot Sober illustrates this perfectly in his staple tome “The Philosophy of Biology” using the long discredited field of phrenology for example. The derivation from bumps on the noggin conclusions about a person’s mental pathology or personality is no longer considered valid by any contemporary scholars, though for a time it was held as valid theory. The change in paradigm did not reveal a flaw in the methodology of the phrenologists, it resulted from the improvement in observational technology which provided data which elucidated the modalities of brain function—we now have an immense wealth of data on neurobiology and the physiology of endocrine processes.      I don’t believe Scientific American gave this a thought of course; I am not insinuating that the author of the report was at all interested in any political agenda, let that he is guilty of homophobia. But consider what the misappropriation of outmoded, outdated science can yield in a propagandist’s hands--there is an article named in "Conservapedia", about “gay bowel syndrome,” that illustrates the problem. From Conservapedia:   Gay bowel syndrome, which has also been described as gay bowel disease, was named as an illness in 1976 in the medical literature via the journal Annals of Clinical and Laboratory Science and in 2004 Medscape stated that gay bowel syndrome is a significant issue in regards HIV infection (The Johns Hopkins HIV Guide website also presently features a literature review article which is essentially a duplicate of the aforementioned article at Medscape). Gay bowel syndrome is a clinical pattern of anorectal and colon diseases which occur with unusual frequency in homosexual patients *(the diseases are not exclusive to male homosexuals)." Starred is the only mention of a caveat. There is, in fact, no statistical link between homosexuality and the acquisition of any disease that is not accounted for by the “cohort factor” “Variation in health status arising from different causal factors to which each birth cohort in a population is exposed as environment and society change.” (MesH)
Here we see a clear case wherein a scientific authority, respected at the time of an article's publication as well as today, is misused by ignoring the context of the cohort.     In completing the grant research for a medical sociology study on telomere attrition, my “side job” while completing my work in cognitive ethology at a university in Birmingham, AL (“Social Status and cellular aging in a multi-ethnic study of children,” Needham), I became quite familiar with the difficulty of extrapolating from data dependent on socio-economic factors over time.      There has been a deluge of research into leukocyte telomere attrition since the Nobel Prize in Physiology or Medicine for 2009 was won by Elizabeth H. Blackburn, Carol W. Greider, and Jack W. Szosta for the study of how chromosomes are protected by telomeres and the enzyme telomerase. Sociologists are attempting to draw relations between socio-economic class and physiological change to cellular telomeres. Telomeres are bodies at the "ends" of chromosome. With each replication telomeres in effect get shorter, and after approximately fifty mitotic cycles the shrinking of these protective structures is too great for them to perform their function, which leads to cell death. A well known example of a dataset, a cohort used for this research, is the Newcastle Thousand Families Study: We investigated the association between telomere length and both cross-sectional and life-course measures of socio-economic status at age 50 in 318 members of a 1947 birth cohort study, the Newcastle Thousand Families Study. This cohort includes all live born singletons born in May and June 1947 in the city of Newcastle upon Tyne, UK (n = 1147) (Spence et al., 1954; Miller et al., 1960, 1974). During the 50-year follow-up of these individuals in 1995–1997, data on adult health and lifestyle were collected by self-completion questionnaire and blood was taken (Lamont et al., 1998, 2000; Parker et al., 2003; Pearce et al., 2004). Associations between life-course measures of socio-economic status and self-rated health in this cohort have previously been reported (Adams et al., 2004).” Jean Adams, Carmen Martin-Ruiz, Mark S. Pearce, Martin White , Louise Parker, Thomas Von Zglinicki. No association between socio-economic status and white blood cell telomere length. Aging Cell. Volume 6, Issue 1, pages 125–128, February 2007My relation of the pertinent data for the purposes of research:                                                                               
**Key Terms: Biological Aging, Inequalities, Newcastle Thousand Families, Socio-Economic Factors
       Research focus:  Is there a direct link between socio-economic status and telomere length?
       In a previous study of a large heterogeneous sample of 1552 females aged 18–75 (Cherkas, et al. 2006); association between socio-economic status and white blood cell telomere length was weak, inconsistent.
       Data: Sample-Newcastle Thousand Families Study (NTFS); Time period-May/June 1947 to 1997; Longitudinal meta-analysis included both men and women, unlike the previous study. Data gathered is a combination of self-reported conditions, index-based estimates, and analysis of 1997 blood samples.
        Methods:  Quantitative meta-analysis of a homogenous birth cohort of 318 singletons, born in Newcastle on Tyne, UK, in May- June 1947. Telomere length was compared with socio-economic status determined by both cross-sectional and life-course measures at age 50yr in the 318 members of the NTFS. 
§ Equivalized household income at age 50;
§  number of times in non-manual class;
§  socio-economic trajectory  age 0-25, 25-50, and 0-50;
§  pack years of cigarette smoking;
§  mean rank, dietary antioxidants;
§  Body-mass index;
§  Units of alcohol per week.
       Results: Results are presented for the full participant sample, as well as by gender (for continuity in comparison with Cherkas, et al.’s 2006 findings).
§  After adjustment for lifestyle factors, paternal age at birth, and gender, there appeared no association  between socio-economic  markers and telomere length in the combined cohort, and in the sex-specific analyses there was no statistically significant association.
§  Telomere length found to be longer in men than women
§  No association between smoking and telomere length (this and the previous finding conflict with those of previous studies)
       Conclusions: from these results there seems to be no association between  socio-economic status and telomere length, which does not seem probable given the known association between economic status and morbidity. It is possible that variations in telomere length at birth, for which no data are available, might mask the correlation.
Boring, huh? Really just to get to that italicized bit.      However, in order for researchers to draw valid conclusions about the raw data in an empirical study, such details are necessary about the subject. An apt and honest translator is needed to communicate this message to the general public. There is a project in the making suited well for this purpose, to which I have volunteered my own efforts and encourage other practitioners and researches who wish to retain responsibility for their life’s work to do the same. I was alerted to the existence of Mr. Brown’s endeavour by my good friend Emma, of the blog Neurilemma:      “Barrett Brown has launched the Science Journalism Improvement Program, the first of several efforts being undertaken by the distributed think tank Project PM. Barrett Brown has launched the Science Journalism Improvement Program, the first of several efforts being undertaken and distrubted by the think-tank Project PM. This process begins by enlisting interested scientists and freelancers, all of whom will be included in our database along with information on their areas of interest and expertise; such information will be used to designate journalist-scientist pairs, members of which will together decide on the particulars of the articles to be produced as well as the specific nature of their partnerships. Aside from facilitating the initial introduction and providing any assistance that a pair might request, Project PM and the administrators of the Science Journalism Improvement Program will otherwise refrain from supervising the working relationship of the pair, which will be governed by nothing other than mutual respect and a shared intention to improve the degree of scientific knowledge on the part of the general public.      At this early stage, Project PM has already recruited a handful of prominent freelancers and established scientists to participate in this effort, and the program is now open to applicants of both sorts. If you’re a freelance writer or science-based practitioner interested in working with us, send me a brief e-mail at including a brief history of your work and a list of research interests.” I include below a link to Mr. Brown's article. A Modern Solution to An Age-Old Problem I would personally appreciate your inquiry. Kenneth