The Canadian initiative to stop Wireless Electrical and Electromagnetic Pollution2 April 2014
The C4ST press conference from Ottawa is now available for viewing here (right side of screen):
C4ST is a national, not-for-profit, volunteer-based coalition of parents, citizens and experts.
1) Educate and inform Canadians and policy makers about the dangers of the exposures to unsafe levels of radiation from technology
2) To work with all levels of government to create healthier communities for children and families
Dear Dr. Paul Demers,
I am writing to you following the report you released, having
read your past epidemiological study on non ionizing
radiation, and having seen you in an interview on Canadian TV,
saying that both ionizing and non ionizing radiation are
You said: "There are about 60 substances or exposures, that
are known to cause cancer or for which there is at least a lot
of evidence. Among the risk factors "different types of
radiation, including both ionizing and non ionizing radiation".
I also read what you told to the media. On your panel there
are people with conflicts of interests, for long time, and for
a lot of money. You replaced one of them, as you of course
know. Although others were not disclosed in public it (John
Moulder was exposed in the Canadian Medical Association
Journal), does not make them non existent, it surely does not
make the report totally independent. As for your will to give
the public a sense of control, this sense of control is
unfortunately false sense of security given the fact that
CHRONIC exposure is being FORCED on the public, with an ACUTE
standard. This already makes the acute standard non realistic
for the current situation of exposure. The burden of proof is
on the manufacturers and not on the public.
My impression was that you would be different than the
industry funded people on your panel, and the other ones who
are not known experts from the field, and a member of the
industry-connected ICNIRP, and another one who has a company
on the subject, that protects the acute standard.
The public really does not expect the panel's empathy or
receiving false sense of control, but those who talked on your
conference, just KNOW that the public is being put at risk.
People are asking for scientific integrity, truth, avoiding
conflict or at least disclosing them.
The Bioinitiative group has already proven that the standard
is not protective. They are the known experts in the field,
who have no conflict of interest. The problem with continuing
like this, for another decade, is putting at risk the next
generation. The future of Canada is dependent on the health
status of the children. They are not protected, with Wi-Fi in
schools, with cell phones, they must be protected. How are you
going to do that? Who is taking responsibility in Canada? I
have not seen one public official who is taking
responsibility. And if you investigate the history of the
Royal Society's reports, you will realize that these reports
started when strong members of the public succeeded in raising
awareness of the problem, and they were perceived by the
public health officials as threat to the industry. This is a
tragedy, under the mask of science.
Dear Editor: Wireless radiation safety standards need to protect Canadians
Wireless connectivity is now widely used and accepted throughout
I am concerned that the process for reviewing
Since May of 2013, Canadians for Safe Technology have warned that the Health Canada review process commissioned to the Royal Society has been assigned to an expert panel that was conflicted. This panel is infiltrated by scientists who promote the wireless technology industry, so that the outcome was predetermined to support un-safe guidelines for wireless microwave exposure. For example, after it was reported in the Canadian Medical Association Journal this past summer that the original
C4ST CEO Frank Clegg (formerly president of Microsoft
I have followed some of the submissions made by experts from around the world, including medical doctors from hospitals and universities such as the Women's
Health Minister Ambrose has a duty to ensure that Canadian safety guidelines fully protect our citizens, yet present guidelines are very faulty. It is time for
Rong Wang, PhD, November 13, 2013
As cell phones and other wireless devices become increasingly popular, there is a growing concern over the possible health impact of wireless technology. Science is still inconclusive on whether cell phone radiation is safe or harmful to humans. Consumers are often confused by conflicting study results and mixed media messages. This article is intended to explain the primary causes of the scientific dilemma and offer some suggestions on how to interpret scientific findings in the field of cell phone radiation and human health.
In the past decade, several large epidemiological studies have been carried out around the world to examine possible links between cell phone use and brain cancer. Results from those studies have been mixed and sometimes contradictory. However, following a comprehensive review of the existing scientific evidence, the World Health Organization (WHO) classified cell phone radiation as "possibly carcinogenic to humans" in 2011. The WHO's classification illustrates our current state of knowledge on this issue and calls for more research. The controversy is likely to continue for many years or even decades to come.
In the midst of uncertainty, there are a few things that consumers should be aware of when interpreting the existing and upcoming scientific findings and media messages related to this topic.Study Biases and Methodology Limitations Impair Study Quality
There are numerous sources of biases  involved in epidemiological studies. In one type of study, called a case-control study, prior exposure to cell phone radiation is compared between people with and without brain tumors. Participants are asked to report their cell phone use in the past for an exposure assessment, which can lead to recall bias. In addition, cell phone use habits seem to affect people's likelihood to participate in a study, which can lead to participation or selection bias.
In another type of study, called a cohort study, a group of healthy people with different exposure status (e.g. cell phone users vs. non-users) was followed over time to compare their brain tumor incidence. The prospective cohort study minimizes recall bias but comes with other problems. For example, the Danish Cohort Study, the only cohort study targeting cell phone use and brain cancer risk to date, has a serious misclassification problem (information bias). Among the total of 420,000 cell phone subscribers under study, about 200,000 corporate cell phone users were excluded from the "user" group and were classified into the "non-user" group while in reality they could have been among the heaviest users. Besides, as cell phones and other wireless technologies become more and more universal, it is increasingly difficult to find a truly unexposed control/reference group for risk comparison.
Another common methodological limitation of epidemiological studies is the inaccurate assessment of exposure to cell phone radiation. In the retrospective case-control study, the self-reported cell phone use information can often be inaccurate because it is very difficult for the participants to remember their cell phone use from a long time ago, especially if they were suffering from a brain tumor. Even in the prospective cohort study, an accurate assessment of exposure can still be difficult. For example, the Danish Cohort Study mentioned above used the number of years of cellular subscription instead of actual mobile phone use for exposure assessment. This meant that a person who used a cell phone for five minutes a week was considered to have the same exposure level as a person who spent five hours per day on a cell phone only because they had the same subscription period. Other factors that can further complicate an exposure assessment include different cell phone models (different amount of RF emission), user environment (rural users typically experience greater exposure from their cell phones than urban users), use scenario (e.g. calls made with or without a headset) and other sources of RF exposures (such as cordless phones).
Furthermore, for a rare disease like brain cancer that affects about 20 in every 100,000 people, a large sample size is necessary to produce meaningful and reliable statistical analysis. Studies involving a relatively small number of people are limited in their ability to detect small increases in risk and the results are less reliable.Funding Source and Author Affiliation Influence Study Outcome
In an ideal scientific world, one would expect all studies to be performed with perfect objectivity. However, recent systematic reviews of the influence of financial interests in medical research concluded that there is a strong association between industry sponsorship and pro-industry conclusions. Unfortunately, the same phenomenon has also been shown to be true in the field of cell phone radiation and human health.
In 2006, Dr. Henry Lai, a research professor in the bioengineering department at the University of Washington did an analysis of 326 existing studies on possible biological effects of RF radiation published between 1990 and 2006, and where their funding came from. He found that about 50% of the studies showed a biological effect and 50% did not. But when he filtered the studies into two groups those funded by the wireless industry and those funded independently Lai discovered that industry-funded studies were 30% likely to find an effect, as opposed to 70% of the independent studies. A 2007 systematic review of 59 experimental human studies found a similar phenomenon studies funded exclusively by industry reported the largest number of outcomes, but were 90% less likely (odds ratio 0.11) to report an effect or a link than studies funded by public agencies or charities. A 2010 analysis concerning the same topic showed that the funding source and author affiliation significantly affect whether or not a study shows a correlation between cell phone use and cancer.
To add to the confusion, when a study generates multi-fold findings, its general conclusion or press release may not objectively reflect all aspects of its findings. When citing the findings of a study, different media may use different headlines and emphasize different aspects of the findings. This can be misleading for general public who often rely on media messages to gain understanding.
Therefore, consumers should be aware of the impact of financial interests on science and public issues, and take the funding source and authorship into account when interpreting scientific findings and media messages related to cell phone radiation and human health.Long Latency Impedes Scientific Conclusion
Further complicating the epidemiological evidence is the long latency period between the exposure to carcinogens and the clinical diagnosis of cancer. The recent WHO official classification of outdoor air pollution as a leading cause of cancer (carcinogenic) to humans helps illustrate the issue of long latency. When asked why it had taken so long to reach the conclusion, IARC director Dr. Christopher Wild said that one problem was the time lag between exposure to polluted air and the onset of cancer and "often we're looking at two, three or four decades once exposure is introduced before there is sufficient impact on the burden of cancer in the population to be able to study this type of question." In additional to the long latency between exposure and the diagnosis of cancer, it also takes time for science to gather information, perform analysis, resolve controversy, and finally reach consensus. In the case of cigarettes, it took more than 100 years to definitively link cigarette smoking to lung cancer. Before that, numerous studies had actually concluded that there was no link between cigarettes and cancer.
Cell phones have only become prevalent in the past 15 years. Most of the existing studies have covered only a few years, with very limited cases covering more than 10 years. Therefore, one should not expect to have sufficient evidence to support a link between cell phone radiation and brain cancer, even if it does exist. The controversy is likely to continue for many years or even decades to come. While waiting for the final answer, consumers should not ignore the early evidence of risk  and the lessons that history teaches us when trying to understand the health impact of cell phone radiation.Conclusion
Not all scientific studies should be treated equally in terms of quality and reliability. They can be influenced by multiple factors such as study biases, methodology limitations, funding sources, author affiliations, and latency periods. Consumers should consider all of these factors when evaluating the current body of scientific findings related to cell phone radiation.
 Epidemiology is the study (or the science of the study) of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and informs policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive medicine.
 Biases in research is any factors that produce systematic variations or errors in research findings.
 For example, the 13-country case-control Interphone study has a high refusal rate of the control (41%) it is assumed that healthy (non-cancerous) people who did not use a cell phone were less likely to participate in the study compared to healthy people who used a cell phone and the end result of the selection bias is an underestimate of risk (Interphone study, 2010)
 Lönn 2004 Output power levels from mobile phones in different geographical areas; implications for exposure assessment
 For example, the authors of the children-focused CEFALO study acknowledged that "our study also has limitations because childhood brain tumors are rare, we could eventually include only 352 case patients and about two control subjects for each patient. Thus, the statistical power of the study to detect small risk increases was limited." (The CEFALO report, 2011)
 Bekelman et al. 2003; Yaphe et al. 2001
 For example, in the CEFALO study, both the results and conclusion of the abstract are contradicted by the reported results. The general conclusion in the press release that "children and adolescents who use mobile phones are not at a statistically significant increased risk of brain cancer compared to their peers," is a misrepresentation of the study's actual finding of increased risks. The study was partly funded by the mobile phone industry funded Swiss Research Foundation on Mobile communication and the study coordinator Dr. Martin Röösli is a member of its board.
 Cigarettes had been around in the United States in crude form since the early 1600s and became widely popular after the Civil War (1861-1865). By 1944, the American Cancer Society began to warn about possible ill effects of smoking, although it admitted that "no definite evidence exists" linking smoking and lung cancer. In 1964, a report by the Surgeon General's Advisory Committee on Smoking and Health concluded: "cigarette smoking is causally related to lung cancer in men." In 1965, Congress passed the Federal Cigarette Labeling and Advertising Act requiring the surgeon general's warnings on all cigarette packages.
 For example, the large 13-country Interphone study found no overall increased risk of the brain cancer glioma from cell phone use. However, it observed a 40% increase in risk for people with highest exposures. A 2013 study of 790,000 women in the UK found a possible increased risk of acoustic neuroma in women who had used a cell phone for more than 5 years compared to women who never used a cell phone, and the risk of acoustic neuroma increased with increasing duration of cell phone use.
The Cell Phone-Brain Cancer Controversy
Jason Newfoundland, The Fountain Magazine, Issue 91, Jan-Feb, 2013
In recent years, people have been divided by conflicting studies about the risk of cancer posed by cell phone radiation. Does the current conflicting research eradicate or support the cell phone-cancer controversy?
Cell phone use has shown a dramatic increase in the world during the 1990s. The heated controversy today is about whether there is a relationship between cell phone use and the risk of developing malignant and benign brain tumors. This controversy did not existat least in the eyes of the publicuntil accumulating anecdotal evidence began suggesting a link between cell phone use and cancer. Since the first pieces of anecdotal evidence, numerous studies have investigated the cell phone-brain cancer link and a general summary of the findings is, at best, confusing. The substantial room for improvement in the experimental designs of these studies, the appearance of brain cancer after a long period of exposure, and some conflicts of interest among researchers prevented the results from being conclusive. More recent studies provide growing evidence for the link, suggesting there is reason to be suspicious about the studies that refute the relationship between cell phone use and brain cancer.
Possible health issues regarding exposure to radio frequency (RF) energy were described in a previous Fountain article (Tombak, 2002). This article also stated that proving or disproving the existence of RF exposure's biological hazards remains an issue for epidemiology due to relatively low exposure levels, relatively small populations, and a lack of reliable dose estimates. The National Cancer Institute (NCI) is now maintaining an up-to-date web page to inform the public on key points that can be drawn from epidemiological studies investigating the cell phone-brain cancer link. It would be advisable that individuals concerned about this potential link become familiar with this web page and visit frequently to check the updates. A regular visitor will notice that the language on this page is evolving in every update in a way that the most recent version is less likely than the previous one to discredit the link as "out of the question". This is because we are starting to seealbeit still opposed as weakstronger signs of the alleged link as there is an increase in both the sheer number and the experimental design quality of relevant studies.
The first two key points that NCI draws on concern the type of electromagnetic energy emitted by cell phones, and the factors that determine a users energy exposure level. It would not be surprising if this train of thought followed with a third key point that stated that the cancer risk depended on the amount of energy that each individual was exposed to. However, the third key point quickly draws the conclusion that "studies thus far have not shown a consistent link between cell phone use and cancers of the brain, nerves, or other tissues of the head and the neck." It further states "more research is needed because cell phone technology and how people use cell phones have been changing rapidly".
Regardless of what type of general message one gets from these three key points, I want to emphasize that there is benefit in avoiding a lump-sum conclusion, and in making oneself aware of the results of individual studies. Before I move on to individual studies, however, I will point out how scientifically sound interpretations of statistical power and significance may lead to categorizations as 'non-existent' or 'weak', but how this scientific reasoning can potentially be misleading for the population at large. In this manner, one would better be able to make sense of why cell phone companies are, on one hand, highlighting the studies that have failed to find a causal link between cell phone use and brain cancer, but on the other hand, are taking all legal precautions necessary to prevent a future litigation by inserting a warning slip in fine print that cautions users not to hold the phone closer than a certain distance against one's head or body.
The null vs. the alternative
A statistical hypothesis test involves two hypotheses: the null and the alternative hypothesis. The null hypothesis represents the status quo; it assumes that there is no real difference between the two groups under study and the observed difference can be attributed to random chance. Drawing a parallel with legal systems, the presumption that a defendant is innocent until proven guilty can be interpreted as saying that his or her innocence is the null hypothesis. There has to be sufficient evidence on the contrary, i.e showing the guilt, in order to be able to convict the defendant. In a similar fashion, an epidemiological study investigating the presence of a link between cell phone use and brain cancer would have a null hypothesis that states the absence of such a link. The cell phone technology is assumed to be innocent unless the data prove otherwise.
The alternative hypothesis, the latter of the two, represents the claim that there actually is a statistically significant link between cell phone use and brain cancer, and the observed link cannot be attributed to random chance. In our legal analogy, the alternative hypothesis is laying the charges against cell phone technology, thus as the Latin maxim "semper necessitas probandi incumbit ei qui agit" states, the burden of proof lies with the alternative hypothesis.
As a consequence of this construction, a hypothesis test can have only one of two conclusions. If the data shows results that are beyond some predetermined significance level, the null hypothesis is rejected and the researchers believe that there is sufficient evidence to say that the alternative is true. Such a conclusion would establish a link between cell phone use and brain tumors. On the other hand, if the results do not reach the desired significance level, the conclusion is not the confirmation of the null hypothesis, but a failure to conclude that the alternative is true. In other words, when the desired significance level is not reached, the only outcome is a lack of conclusion; the test would not falsify the null hypothesis but would not declare it to be true either. The accused would be vindicated on the basis of insufficient evidence.
News on the innocence of cell phone technology, or any technology for that matter, should be read primarily with this perspective in mind. The conclusions of research studies are reported on the basis of whether the results "reach or fail to reach significance". However, a more meaningful statistic to report from the study would be the deviation of the results from significance, if they were not significant. Results that are close to statistical significance can still be "meaningful". After all, the significance level chosen for most studies relies more on traditional scientific habits than anything else. In this perspective, it can even be called arbitrary. In reality, we may not have expertise in today's world to determine whether a 5% significance level is more meaningful than a 10% when it comes to studying the link between cell phone use and brain cancer. So when the NCI officials mention "lack of a consistent link," all of what they mean is that the desired significance level has not been reached in most credible and up-to-date studies. Yet, the public is not informed about how significant the results were. Furthermore, as we see in the much-acclaimed Interphone study, failure to reach significance in the entire study may be overshadowing the fact that significance was attained for a subgroup of people, for instance, the top 10% of the population with highest cell phone use (The Interphone study group, 2010).
Perspectives on brain cancer risk
News regarding cell phone tumor risks is plainly confusing because a battle continues among different international panels and interest groups over how to analyze and interpret cell phone tumor data. An article (July 6, 2011) on Microwave News explains why there is no overlap in the conclusions made by the International Commission for Non-Ionizing Radiation Protection (ICNIRP) and the International Agency for Research on Cancer (IARC), the two panels that are supposed to work together, but fell into deep disagreement as the data started showing some link between cell phone use and brain cancer. This piece is a highly suggested read for anyone who would like to be able to make more sense of the past and potentially future news on cell phone tumor risks.
The Interphone study
Much of the current debate on cell phone tumor risks actually revolve around the Interphone study, which was conducted by a consortium of researchers from 13 countries, and is the largest health related case control study of the use of cell phones and head and neck tumors. According to NCI's summary, "most published analyses from this study have shown no statistically significant increases in brain or central nervous system cancers related to higher amounts of cell phone use. One recent analysis showed a statistically significant, albeit modest, increase in the risk of glioma among the small proportion of study participants who spent the most total time on cell phone calls. However, the researchers considered this finding inconclusive because they felt that the amount of use reported by some respondents was unlikely and because the participants who reported lower levels of use appeared to have a reduced risk of brain cancer."1
The general message that comes across in NCI's summary of Interphone results is that we do not have enough reason to believe that cell phones are dangerous. However, it is very important to remember that one can never accept the null hypothesis that "cell phones are safe." The only conclusion that can be drawn is on the basis of insufficient evidence, which is to say that cell phones are dangerous since the desired significance level has not been reached.
As the Interphone study is the largest of its kind, it has drawn substantial attention from concerned parties, and a significant part of this attention has been in the form of harsh criticisms for the experimental design, data analysis, and stated conclusions. For instance, one of Interphone's biggest critics, the International Electromagnetic Field (EMF) Collaborative, published a paper in May 2010 detailing the flaws of the study. Among other things, these flaws included using data from 2004 and before when cell phone use was much less common, categorizing subjects who used cordless phones (which emit the same microwave radiation as cell phones,) as 'unexposed'; exclusion of many types of brain tumors; exclusion of people who had died, or were too ill to be interviewed, as a consequence of their brain tumor; and exclusion of children and young adults who are more vulnerable.
In August 2009, more than forty leading independent scientists, physicians and other experts from fourteen countries endorsed the white paper "Cell-phones and Brain Tumors: 15 Reasons for Concern, Science, Spin and the Truth Behind Interphone" by US researcher Lloyd Morgan. Investigating the research on cell phone tumor risks including the Interphone study, this paper concluded that "there is a risk of brain tumors from cell phone use; telecom funded studies underestimate the risk of brain tumors; and children have larger risks than adults for brain tumors". Unlike the Interphone study, some industry funded research also accepts the risks associated with cell phone use. In 1999, Dr. George Carlo, head of a $25m research body funded by the mobile phone industry in the US, said his study showed an increased risk of getting a type of rare brain tumor from using mobile phones. This early in the debate, he was probably one of the first researchers with links to industry who stopped ruling out the tumor risks of cell phones.
A review of other main studies
Hardell et al.
Dr. Lennart Hardell, from Örebro University in Sweden, is one of the most adamant leaders in cautioning the world about cell phone tumor risks. In 2007, he and his team reported that cell phone users were at an increased risk of malignant glioma, and that a daily one-hour exposure significantly increased the risk for developing a brain tumor after 10 years (Hardell et al., 2007). In a more recent study also cited by NCI, they found statistically significant trends of increasing brain cancer risk for the total amount of cell phone use and the years of use among people who began using cell phones before the age of 20 (Hardell et al., 2011). They also published a number of other papers in epidemiological journals pointing to the risks associated with cell phone and cordless phone usage.
The Danish cohort study
A 2011 cohort study in Denmark linked billing information from more than 420,000 cell phone subscribers with brain tumor incidence data from the Danish Cancer Registry (Frei et al., 2011). This study was an update on the 2006-update of a 2001 cohort study (Schüz et al., 2006; Johansen et al., 2001) that has been dogged by controversy and political suspicions since the first results were published ten years ago. NCI cites the study and states that the analyses found no association between cell phone use and the incidence of glioma, meningioma, or acoustic neuroma, even among people who had been cell phone subscribers for 10 or more years. However, there is no mention of the published or vocal criticisms of the study.
The main criticism for the study is that more than 200,000 corporate mobile subscribers were excluded from the cohort as cell phone bills were not in users' names. Microwave News states, "In the time period covered in the Danish projectfrom 1987 through 1995cell phones were expensive and it's no stretch to assume that those who did not have to pay their own bills racked up the most talk time."2 Thus, the study designers effectively removed one-third of the population with the heaviest cell phone use. Dr. Lennart Hardell had also criticized the original 2001 paper by publishing on the shortcomings that make the conclusions premature (Hardell and Mild, 2001). Concerning the 2011 update, the Microwave News bluntly suggests, "Don't believe a word of it".
It is also interesting to note that the results came just five months after a panel of experts from the World Health Organization's International Agency for Research on Cancer (IARC) deemed cell phones a possible cause of cancera statement that sparked fear in many of the world's 5 billion cell phone users.
While there is still no established causal link between cell phone use and cancer, we know as a fact that different research groups have found an increased risk of a rare type of brain cancer among heavy users. Even though children are known to be at a greater risk because of being in earlier stages of neural development, it is unfortunate that data from children were not included in studies until very recently. Concerned citizens of the world need to raise awareness about the behind-the-scenes battle taking place between different international panels and interest groups. This will make a reliable interpretation of conflicting news more possible. Further corroboration for both statistical and anecdotal evidence on the relationship between cell phone use and brain cancer may be necessary to "prove" a link, but this should, by no means, be interpreted as a vindication of cell phones. In the meantime, it is only safe to take precautions oneself, and encourage loved ones to reduce exposure to electromagnetic energy from cell phones by using a hands-free device and by reserving the use of cell phones for shorter conversations.
Frei P, Poulsen AH, Johansen C, et al. 2011. "Use of mobile phones and risk of brain tumours: update of Danish cohort study." British Medical Journal; DOI: 10.1136/bmj.d6387.
Hardell, L., Walker, M. J., Walhjalt, B., Friedman, L. S. and Richter, E. D. 2007. "Secret ties to industry and conflicting interests in cancer research." American Journal of Industrial Medicine,; 50: 227233. doi: 10.1002/ajim.20357.
Hardell L, Carlberg M, Soderqvist F, Hansson-Mild K, Morgan LL. 2007. "Long-term use of cellular phones and brain tumours: Increased risk associated with use for > or = 10 years." Occup Environ Med. 64:626632.
Hardell L, Carlberg M, Hansson Mild K. 2011. "Pooled analysis of case-control studies on malignant brain tumours and the use of mobile and cordless phones including living and deceased subjects." International Journal of Oncology; 38(5):14651474.
Hardell L, Mild KH. 2001. "Re: Cellular Telephones and Cancera Nationwide Cohort Study in Denmark"; JNCI J Natl Cancer Inst. 93(12): 952.
Johansen C, Boice Jr. JD, McLaughlin JK, Olsen JH. 2001. "Cellular telephones and cancer: a nationwide cohort study in Denmark." Journal of the National Cancer Institute; 93(3):203207.
Schüz J, Jacobsen R, Olsen JH, et al. 2006. "Cellular telephone use and cancer risk: update of a nationwide Danish cohort." Journal of the National Cancer Institute; 98(23):17071713.
Tombak, Ali. 2002. "Biological Effects of Cellular Phones." The Fountain, 37 (1).
The Interphone Study Group. 2010. "Brain tumour risk in relation to mobile telephone use: results of the Interphone international case-control study." International Journal of Epidemiology; 39(3):675694.