EpidemiologicEpidemiological Researchal Research

EpidemiologyEpidemiology

A branch of medical science that A branch of medical science that deals with the incidence, distribution, deals with the incidence, distribution, and control of disease in a populationand control of disease in a population

-- Merriam-Webster’s Collegiate Dictionary, 10-- Merriam-Webster’s Collegiate Dictionary, 10thth Edition Edition

EpidemiologyEpidemiology Epidemiological studies look at populations Epidemiological studies look at populations

to investigate potential associations between to investigate potential associations between aspects of health (such as cancer and heart aspects of health (such as cancer and heart disease) and diet, lifestyle, genetics, or other disease) and diet, lifestyle, genetics, or other factors within populationsfactors within populations

Yields information about the distribution and Yields information about the distribution and determinants of disease or other health determinants of disease or other health outcomes, but does not establish cause and outcomes, but does not establish cause and effecteffect

Non Randomized due to ethical concernsNon Randomized due to ethical concerns

--International Food Information Council, 2002 --International Food Information Council, 2002

Research DesignsResearch Designs Prospective StudiesProspective Studies

– Monitor a group of people over a period Monitor a group of people over a period of time to observe effects of diet, of time to observe effects of diet, behavior, and other factors on health or behavior, and other factors on health or the incidence of diseasethe incidence of disease

Retrospective StudiesRetrospective Studies– Look at events and behaviors that have Look at events and behaviors that have

already taken placealready taken place--International Food Information Council, 2002 --International Food Information Council, 2002

Research DesignsResearch DesignsResearch may also be either observational Research may also be either observational

or experimentalor experimental

OBSERVATIONALOBSERVATIONAL– Suggests Suggests

associations or associations or correlations correlations between between characteristics characteristics based on observed based on observed differencesdifferences

EXPERIMENTALEXPERIMENTAL

-Part of a population -Part of a population receives some sort of receives some sort of treatment and the results treatment and the results are compared with the are compared with the results of a control groupresults of a control group

-must be conducted to -must be conducted to determine cause and determine cause and effecteffect

--International Food Information Council, 2002--International Food Information Council, 2002

Journal ArticleJournal Article

Case-Control Study of Case-Control Study of Lifetime Physical Lifetime Physical Activity and Breast Activity and Breast Cancer RiskCancer Risk

found in found in American Journal of American Journal of Epidemiology Epidemiology vol 154, No. 4, 2001vol 154, No. 4, 2001

AUTHORSAUTHORS– C.M. FriedenreichC.M. Friedenreich– H.E. BryantH.E. Bryant– K.S. CourneyaK.S. Courneya

AFFILIATIONSAFFILIATIONS RESEARCH METHODSRESEARCH METHODS

– Population based control study Population based control study – EligibilityEligibility– ControlsControls

RESEARCH QUESTIONRESEARCH QUESTION

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

Interviews were conducted with all Interviews were conducted with all participantsparticipants– Questions were asked regarding menstrual Questions were asked regarding menstrual

and reproductive histories, personal and reproductive histories, personal history and family histories of breast history and family histories of breast cancer, alcohol consumption, diet and cancer, alcohol consumption, diet and height, weight and waist and hip height, weight and waist and hip circumferencescircumferences

– Physical activity patterns were examined Physical activity patterns were examined through a questionnaire assessing through a questionnaire assessing occupational, household and recreational occupational, household and recreational activityactivity

Study DesignStudy Design

QuestionnaireQuestionnaire– Physical activity patterns were Physical activity patterns were

examined through a questionnaire examined through a questionnaire assessing occupational, household and assessing occupational, household and recreational activityrecreational activity

– Self-report lifetime frequency, duration, Self-report lifetime frequency, duration, and intensityand intensity

– MET values were determined on the MET values were determined on the basis of the description of the activitybasis of the description of the activity

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

research questionresearch question

MAJOR FINDINGSMAJOR FINDINGS– Cases and controls had similar socio-Cases and controls had similar socio-

demographic and anthropometric demographic and anthropometric characteristics, as well as medical and characteristics, as well as medical and reproductive historiesreproductive histories

– Decreased risk with increasing activity Decreased risk with increasing activity was found in postmenopausal women was found in postmenopausal women onlyonly Total lifetime activity was associated with a Total lifetime activity was associated with a

30% reduction in breast cancer risk for 30% reduction in breast cancer risk for postpostmenopausal women (not found in menopausal women (not found in prepremenopausal women)menopausal women)

– Strong risk reductions were found for Strong risk reductions were found for both occupational and household both occupational and household activity but not for recreational activityactivity but not for recreational activity

– Reduced breast cancer risk was found in Reduced breast cancer risk was found in women who had not consumed alcohol women who had not consumed alcohol in their lifetimes and also who were not in their lifetimes and also who were not current cigarette smokerscurrent cigarette smokers

Brief CritiqueBrief Critique WeaknessesWeaknesses

– SampleSample – Selection BiasSelection Bias

Threats to External ValidityThreats to External Validity

Threats to Internal ValidityThreats to Internal Validity– Non probability samplingNon probability sampling– The sample was stratified to pre and postThe sample was stratified to pre and post

Weaknesses cont…Weaknesses cont…– Study DesignStudy Design

InterviewInterview

QuestionnaireQuestionnaire– ““Retrospective Contamination” (Kolt and Kirby, Retrospective Contamination” (Kolt and Kirby,

1994)1994)– Misclassification of exposure to lifetime exercise Misclassification of exposure to lifetime exercise

because of self-reportbecause of self-report– Ability of the study to demonstrate an effect of Ability of the study to demonstrate an effect of

physical activity on breast cancer is decreasedphysical activity on breast cancer is decreased ““Nondifferential Misclassification”, therefore Nondifferential Misclassification”, therefore

would underestimate the true effectwould underestimate the true effect

Weaknesses cont...Weaknesses cont...– Statistical AnalysisStatistical Analysis

Huge list of confounders (effect modifiers)Huge list of confounders (effect modifiers)– Threatens External Validity because of multiple Threatens External Validity because of multiple

variable interferencevariable interference

– List of confounders:List of confounders:

Age, BMI, waist-hip ratio, marital status, education Age, BMI, waist-hip ratio, marital status, education level, ethnicity, family history of breast cancer, level, ethnicity, family history of breast cancer, whether menstruation had ever ceased for whether menstruation had ever ceased for reasons besides pregnancy, irregular menstrual reasons besides pregnancy, irregular menstrual cycles, oral contraceptive use, etc.cycles, oral contraceptive use, etc.

Weaknesses cont….Weaknesses cont….– ResultsResults

What’s the dose?What’s the dose? Definition and difference between the three Definition and difference between the three

types of activities and do these interact with types of activities and do these interact with each other at all?each other at all?

Hypotheses Hypotheses – Sample was too small to preclude detection of Sample was too small to preclude detection of

any association related with endogenous estrogen any association related with endogenous estrogen exposureexposure

– No measures were taken to measure relationship No measures were taken to measure relationship between insulin-like growth factors, and immune between insulin-like growth factors, and immune functionfunction

Alternative ExplanationsAlternative Explanations

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

Ideas for Future ResearchIdeas for Future Research

A randomized control trial that A randomized control trial that investigates Quality of Life outcomes investigates Quality of Life outcomes in Breast Cancer Survivors as a result in Breast Cancer Survivors as a result of exercise interventionof exercise intervention

Measure the effects of physical Measure the effects of physical activity on the facilitation or ability to activity on the facilitation or ability to sustain remission of cancer in these sustain remission of cancer in these survivorssurvivors

Epidemiological Research can also Epidemiological Research can also ......

Address issues that go beyond Address issues that go beyond individuals targeting whole individuals targeting whole communities and populations communities and populations

Address wide spread occurrences, Address wide spread occurrences, treatments and issues that a treatments and issues that a population or community may facepopulation or community may face– Ex) - Ex) - Improving health of a populationImproving health of a population

– Improving standard of livingImproving standard of living– Determining the effectiveness of different Determining the effectiveness of different

treatments treatments – Determining norms of a cultureDetermining norms of a culture– Different trends that occurDifferent trends that occur