Epidemiological Research

Epidemiology A branch of medical science that deals with the incidence, distribution, and control of disease in a population A branch of medical science that deals with the incidence, distribution, and control of disease in a population -- Merriam-Webster’s Collegiate Dictionary, 10 th Edition

Epidemiology Epidemiological studies look at populations to investigate potential associations between aspects of health (such as cancer and heart disease) and diet, lifestyle, genetics, or other factors within populations Epidemiological studies look at populations to investigate potential associations between aspects of health (such as cancer and heart disease) and diet, lifestyle, genetics, or other factors within populations Yields information about the distribution and determinants of disease or other health outcomes, but does not establish cause and effect Yields information about the distribution and determinants of disease or other health outcomes, but does not establish cause and effect Non Randomized due to ethical concerns Non Randomized due to ethical concerns --International Food Information Council, 2002

Research Designs Prospective Studies Prospective Studies –Monitor a group of people over a period of time to observe effects of diet, behavior, and other factors on health or the incidence of disease Retrospective Studies Retrospective Studies –Look at events and behaviors that have already taken place --International Food Information Council, 2002

Research Designs Research may also be either observational or experimental OBSERVATIONAL –Suggests associations or correlations between characteristics based on observed differences EXPERIMENTAL -Part of a population receives some sort of treatment and the results are compared with the results of a control group -must be conducted to determine cause and effect --International Food Information Council, 2002

Journal Article Case-Control Study of Lifetime Physical Activity and Breast Cancer Risk Case-Control Study of Lifetime Physical Activity and Breast Cancer Risk found in American Journal of Epidemiology vol 154, No. 4, 2001 found in American Journal of Epidemiology vol 154, No. 4, 2001

AUTHORS AUTHORS –C.M. Friedenreich –H.E. Bryant –K.S. Courneya AFFILIATIONS AFFILIATIONS RESEARCH METHODS RESEARCH METHODS –Population based control study –Eligibility –Controls

RESEARCH QUESTION RESEARCH QUESTION The associations between physical activity and breast cancer risk are quite complex, reflecting the complicated and multiple biologic mechanisms that are likely operative. This study is designed to address some of the unanswered questions regarding the type and dose of activity and the time periods in life when physical activity may be specifically associated with breast cancer risk.

Interviews were conducted with all participants Interviews were conducted with all participants –Questions were asked regarding menstrual and reproductive histories, personal history and family histories of breast cancer, alcohol consumption, diet and height, weight and waist and hip circumferences –Physical activity patterns were examined through a questionnaire assessing occupational, household and recreational activity Study Design

Questionnaire Questionnaire –Physical activity patterns were examined through a questionnaire assessing occupational, household and recreational activity –Self-report lifetime frequency, duration, and intensity –MET values were determined on the basis of the description of the activity

The authors of this article used a RETROSPECTIVE, epidemiological approach in attempts to answer the research question

MAJOR FINDINGS MAJOR FINDINGS –Cases and controls had similar socio- demographic and anthropometric characteristics, as well as medical and reproductive histories –Decreased risk with increasing activity was found in postmenopausal women only  Total lifetime activity was associated with a 30% reduction in breast cancer risk for postmenopausal women (not found in premenopausal women)

–Strong risk reductions were found for both occupational and household activity but not for recreational activity –Reduced breast cancer risk was found in women who had not consumed alcohol in their lifetimes and also who were not current cigarette smokers

Brief Critique Weaknesses Weaknesses –Sample –Selection Bias  Threats to External Validity  Threats to Internal Validity –Non probability sampling –The sample was stratified to pre and post

Weaknesses cont… Weaknesses cont… –Study Design  Interview  Questionnaire –“Retrospective Contamination” (Kolt and Kirby, 1994) –Misclassification of exposure to lifetime exercise because of self-report –Ability of the study to demonstrate an effect of physical activity on breast cancer is decreased  “Nondifferential Misclassification”, therefore would underestimate the true effect

Weaknesses cont... Weaknesses cont... –Statistical Analysis  Huge list of confounders (effect modifiers) –Threatens External Validity because of multiple variable interference –List of confounders: Age, BMI, waist-hip ratio, marital status, education level, ethnicity, family history of breast cancer, whether menstruation had ever ceased for reasons besides pregnancy, irregular menstrual cycles, oral contraceptive use, etc.

Weaknesses cont…. Weaknesses cont…. –Results  What’s the dose?  Definition and difference between the three types of activities and do these interact with each other at all?  Hypotheses –Sample was too small to preclude detection of any association related with endogenous estrogen exposure –No measures were taken to measure relationship between insulin-like growth factors, and immune function

Alternative Explanations Alternative Explanations –Weight loss regardless of means may be just as effective in reducing risk of breast cancer (nutrition)

Ideas for Future Research A randomized control trial that investigates Quality of Life outcomes in Breast Cancer Survivors as a result of exercise intervention A randomized control trial that investigates Quality of Life outcomes in Breast Cancer Survivors as a result of exercise intervention Measure the effects of physical activity on the facilitation or ability to sustain remission of cancer in these survivors Measure the effects of physical activity on the facilitation or ability to sustain remission of cancer in these survivors

Epidemiological Research can also... Address issues that go beyond individuals targeting whole communities and populations Address issues that go beyond individuals targeting whole communities and populations Address wide spread occurrences, treatments and issues that a population or community may face Address wide spread occurrences, treatments and issues that a population or community may face –Ex) - Improving health of a population –Improving standard of living –Determining the effectiveness of different treatments –Determining norms of a culture –Different trends that occur