Melissa Friesen, Ph.D.
|Organization:||National Cancer InstituteDivision of Cancer Epidemiology & Genetics, Occupational and Environmental Epidemiology|
|Address:||Executive Plaza SouthRoom 8106|
Dr. Friesen received a Ph.D. (2006) and M.Sc. (2001) in occupational hygiene from the University of British Columbia in Vancouver, Canada. She completed post-doctoral studies at Monash University in Melbourne, Australia, and at the University of California at Berkeley. She joined the NCI as a tenure-track investigator in the Occupational and Environmental Epidemiology Branch in June 2009.
Dr. Friesen's research has focused on quantitative assessment strategies to minimize exposure misclassification in occupational epidemiologic studies. Using quantitative exposure estimates in epidemiologic studies is a well-recognized method of reducing the exposure misclassification that results in attenuated exposure-response relationships; however, their use does not completely eliminate exposure misclassification. She has focused on improving exposure estimates, evaluating the robustness of exposure-response relationships to exposure assessment strategies, and using statistical models for both developing exposure metrics and evaluating their exposure-response relationships. By using more refined and more proximal exposure measures, her research has resulted in quantitative exposure-response relationships for several exposure - disease associations that have not previously been published.
Critical aspects for refining exposure estimates have been the use of pilot studies, validation studies, and supplementary information to refine exposure estimates to reflect the more proximal exposure of interest. For example, in the British Columbia Sawmill Cohort, the resin acid content of the particulates measured in the sawmill environment was used to develop factors to adjust for the presence of non-wood dust sources of particulate by work area. In the British Columbia Aluminum Smelter Cohort, the factors that influenced the relationship between two common measures of polycyclic aromatic hydrocarbon exposure (BSM and BaP) and the other specific PAHs were evaluated to provide an indication of the misclassification that could occur if these factors were not taken into account.
At OEEB, Dr. Friesen extends her research from industry-based studies to population-based studies. She continues to examine and validate methods to refine generic exposure measures to more proximal measures of the dose and the causal components. She identified that using multiple raters, instead of a single rater to rate exposure levels can substantially improve the validity of subjective ratings by harnessing the independent ‘wisdom of the crowds’. However, it is time-consuming to use panels of raters and it is also difficult to find experienced raters, so she continues to examine how to use the raters more effectively. She has also developed a method to use data mining methods (e.g. classification and regression trees, CART) to extract underlying (but not explicitly stated) decision rules from the relationship between exposure estimates derived from professional judgment and questionnaire responses. The resulting CART decision trees extract the valuable information from previous assessments and thus allow the decision rules to be used to estimate exposure in other studies with similar exposure information. As a result, exposure assessors can focus their attention on the exposure scenarios identified by the CART model as being difficult to assess and on scenarios that were not covered by the decision rules. Most importantly, identifying the decision rules removes the assessment from its much criticized ‘black box’. In addition, Dr. Friesen is now extending the use of statistical models that are commonly used in industry-based studies to predict historical exposure to population-based studies. For example, she has developed a framework to combine subjective ratings of exposure from job exposure matrices (JEMs) and exposure measurements to better discriminate between time and job differences in exposure levels in population-based studies.
During the Environmental Exposures and Women's Health seminar series held on October 5, 2010, Dr. Friesen discussed the importance of examining cancer risk separately in men and women. Specifically, she focused on sex differences in the accuracy of exposure assessment tools for epidemiologic studies. View her presentation.