Study of UK Cancer-Moderate-Consumption Paper Shows Fundamental Flaws In Data, Sample Selection, Methodology

Even a cursory examination of “Moderate Alcohol Intake and Cancer Incidence in Women” (published in the Feb. 24 online issue of the Journal of the National Cancer Institute) reveals flawed methodology and other contradictions that call into question the validity of its conclusions.

In the study, Naomi Allen, D.Phil., of the University of Oxford, U.K., and her co-authors, based their conclusions on their analysis of data from the Million Women Study, which included 1,280,296 middle-aged women in the United Kingdom.

SELF-SELECTED SAMPLES UNREPRESENTATIVE

The Allen paper said that their data came from questionnaires completed by 1.3 million, middle-aged women who attended breast cancer screening clinics in the U.K.

The method for selecting the study sample could be its largest flaw.

The Million Women Study web site shows that it is a voluntary, self-selecting study. Self-selecting samples represent a subset of any given population: those sufficiently motivated (for unknown reasons) to take the time and effort to participate. Self-selecting sample populations can often have little connection to reality because they are unrepresentative of a population as a whole.

Indeed, there is no way to know whether or not the women most motivated to participate in this study were those with existing or potential hereditary health problems.

QUESTIONAIRES: EXTENSIVE AND COMPLICATED

According to another page of the web site, “Women were sent the initial Million Women Study questionnaire with their invitation to attending the National Health Service Breast Screening Programme at participating centres across the country.

“Approximately 3 years after completing the first questionnaire, participants were sent a second “update” questionnaire to keep track of their health and to ask new questions about factors such as diet, family history, vitamins and supplements and early life experiences.”

In addition to being voluntary,  self-reporting and spaced over three years, the questionnaires themselves are long, involved, require a substantial span of concentration and only peripherally address the issue of alcohol consumption.

The time- and thought-consuming nature of the questionnaires could make the ultimate sample even less representative.

SELF-ADMINISTERED QUESTIONNAIRES UNRELIABLE

One top data research expert who has served as head of research for one of the “Big Three” American television networks, looked at the Million Women Study questionnaires and told Wine Industry Insight that: “The other problem, obviously, is that it is a self-administered Q (questionnaire), which has virtually zero reliability.  Not that people don’t use them, they just aren’t as reliable as one filled out by a live interview.”

ABSTAINERS EXCLUDED FROM SAMPLE

According to the paper, “Women who reported drinking no alcohol at the time they joined the study may be a biased group as some may have stopped drinking due to ill heath. Therefore, women who reported drinking some alcohol, but less than or equal to 2 drinks per week, were taken as the reference group.”

The issue  of the “sick abstainer” has been well known in research circles for more than two decades and has effectively been corrected for in landmark studies in The Lancet, British Medical Journal, New England Journal of Medicine and others. The inability of the Million Women Study to comply with the established methodology leaves it without a valid “zero consumption” baseline.

NO DISCUSSION OF KEY SOCIOECONOMIC FACTORS

While the paper makes two cursory mentions of adjustments for socioeconomic factors, it devotes no discussion at all to significant factors related to breast cancer: namely income, education, body mass and onset of first pregnancy.

While the paper notes that:

“Women who drank alcohol were likely to be younger, leaner, more affluent, and to do strenuous exercise more frequently than nondrinkers.”

And “Women who drank wine exclusively also tended to be more affluent, to be leaner, or to take strenuous exercise more frequently and were less likely to be current smokers compared with other drinkers.”

Current research has consistently found that the more educated and affluent women are, the more likely they are to have no children or to have their first pregnancy at an older age. And a delayed onset of the first pregnancy is a documented risk for women’s breast cancer.

The authors’ failure to discuss how they handled this issue casts yet another shadow on the study’s conclusions.

Wine Industry Insight will continue to examine the original article.