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362 Statistics and public health researchchanges in hormone therapy practices have led, for example, to about 15,000to 20,000 fewer women developing breast cancer each year since 2003 in theUnited States alone, along with tens of thousands of additional such womenelsewhere in the world.Moving to another public health topic, obesity is the epidemic of our time.It is clear that overweight and obesity arise from a sustained imbalance overtime in energy consumed in the diet compared to energy expended at rest andthrough physical activity. Obesity is an established risk factor for many ofthe chronic diseases that are experienced in great excess in Western societies,including vascular diseases and several major cancers, and diabetes. However,specific knowledge from nutritional or physical activity epidemiology as towhich dietary and activity patterns can be recommended are substantiallylacking and, at any rate, are not sufficiently compelling to stimulate the societalchanges that may be needed to begin to slow and reverse the obesityepidemic. For example, needed changes may involve personal choices in foodselection, preparation and consumption patterns; choices away from a sedentarylifestyle; food supply and distribution changes; changes in city design;restrictions in advertising; and taxation changes, to cite but a few. Of course,favorable dietary and physical activity patterns may have health benefits thatgo well beyond normal weight maintenance.The remainder of this short contribution will elaborate some of the researchbarriers to public health research progress in some areas just mentioned, withfocus on statistical issues.32.3 Biomarkers and nutritional epidemiologyWhile other application areas also grapple with exposure assessment issues,these problems appear to dominate in the nutritional epidemiology researcharea. For example, an international review (World Health Organization, 2003)of nutritional epidemiology research identified few dietary exposures that areassociated with vascular diseases or cancer, with most reports based on selfreporteddiet, typically using a food frequency questionnaire (FFQ) approachwhere the study subject reports consumption frequency and serving size overthe preceding few months for a list of foods.A lack of consistency among epidemiological reports on specific dietary associationshas stimulated a modest focus on dietary assessment measurementerror over the past 25–30 years. Much of this work has involved comparisonsof FFQ data to corresponding data using other self-report tools, such as 24-hour dietary recalls (24-HRs), or several days of food records, to examine FFQmeasurement error properties. However, for a few important dietary factors,including total energy consumption and protein consumption, one can obtainobjective dietary assessments, at least for relativity short periods of time,