MicroBio 160 1st Edition Lecture 9Outline of Last Lecture I. Typical Cancer Progression II. Primary and Secondary Cancer III. Cancer Spread and Mortality IV. How Cancer Spreads V. TheMetastatic Process VI. Vasculogenesis vs. AngiogenesisVII. Tumors need Blood Vessels to GrowVIII. Cancer Cells Produce Angiogenesis-Stimulating Molecules IX. Treating Cancer by Inhibition of AngiogenesisX. Tumor AngiogenesisOutline of Current Lecture I. What is Epidemiology?II. The Epidemiological ApproachIII. Epidemiological StudyIV. How do we Evaluate Evidence V. Comparison of Disease in Different Locations VI. What’s the Difference?VII. The Effect of BiasVIII. Limitations of EpidemiologyIX. Types of EpidemiologyX. The Epidemiologic TriadXI. Main Causes of CancerCurrent LectureWhat is Epidemiology?These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Epidemiology is the study of relationships—it can never prove anything because it is just observations- Epidemiology is the study of patterns, causes and effects of health and disease in defined populationso Uses the causes and risk factors of disease to propose effective strategies for disease prevention and control Make an observation, collect data, and figure out if it is above average o **You can never conclusively say there is a cause The Epidemiological Approach:- It attempts to determine if an observed difference is a real difference—if it is, then it tries to determine why there’s a differenceo Gather Evidenceo Form a hypothesiso Test hypothesis If the statistics support the hypothesis—make recommendations for changes that will protect the public If the statistics don’t support the hypothesis—either revise hypothesis or not o Multiple analysis may generate conflicting reports—distrust and skepticismAn Epidemiological Study How to Evaluate Evidence?—After you run all statistical test, what are the chances there is a link?Observations:- Pollution from chemical factory makes Chemtown stink- 100 cases of bladder cancer in Cleantown- 200 cases of bladder cancer in ChemtownHypothesis:- Chemical pollutants in the air cause people to develop bladder cancer at a higher rate in Chemtown- P value is a statistical testo Estimates the probability that an observed difference would appear by chance even if no difference existso Calculating a p value will tell us if there is a real difference in the rate of cancer development or if it just looks like there is- Statistical significanceo Likelihood that observed difference is real P value= .05 means 5% chance difference is false and a 95% chance that difference is realCancer in Chemtown vs. Cleantown- Are the people in Chemtown at a higher risk for developing cancer than people that live in Cleantown just because they live in Chemtown.o Epidemiologists decide to evaluate Chemtown and gather evidence—they are trying to determine if the number of cancer cases that have occurred in Chemtown is significantly greater than the expected number of cases, given the age, gender, and racial distribution of the group of people at risk of developing the disease o They then calculate the expected number of cases and compare that number with the observed number of cases If the calculated numbers are different then they compare the numbers todetermine if the difference is statistically significant—this generates a p valueResearch Group 1: Hypothesize that living in Chemtown does put one at a significantly higher risk of developing bladder cancerResearch Group 2: Hypothesize that living in Chemtown does not put one at a significantly higher risk of developing bladder cancerTheir calculated p value is .03 – Is their data significant?Their calculated p value is .07– Is their data significant?It depends on how sure the 2 groups want to be that they either are (group 1) or are not (group 2) detetcting a real difference between the expected and actual rates of cancer development in Chemtown.They both want to be able to prove their hypothesis. Thus, they both set their minimumacceptable p value for significance at .05, a fairly stringent level. Yes because their calculated p value is LOWER than .05No because their calculated p value is HIGHER than .05They are both right because Group 1 said it was .03 because it was under .05. Group 2 is right also because they stated that it was going to be above.Why the Difference? Bias is a likely cause:- Experimenter bias: preconceptions influence results- Detection bias: methods are unequal (distribution)- Selection bias: nonrandom volunteering (may not volunteer to do survey)- Recall bias: self reporting errors- Publication bias:o Relationship= publisho No relationship= no publisho 20 stories, 19 show no relationship while 1 shows a relationship (a misleading story is the one published)- If the p value is .05 then 5% of the time we are misled Limitations of Epidemiology:- Epidemiology studies can never prove causation; it cannot prove that a specific risk factor actually causes the disease being studiedo Evidence can only show that a risk factor is associated with a higher incidence of disease in the populationo The strength of the study depends on the number of cases and controls included in the study (p value stronger)—the more cases you get the stronger the p valueTypes of Epidemiology:- Observational: Cleantown vs. Chemtown- Experimental: human equivalent of animal testing—providing or withholding a substance to determine its toxic or beneficial effectso Limited by ethical and legal considerations as well as difficulties securing the cooperation of a large number of people- Descriptive: analyzes data on the distribution and extent of health problems in various populationso Attempts to find correlations among characteristics such as diet, air quality and occupationo Comparisons are frequently made between countries and smaller geographic regionso Attempts to uncover and portray the occurrence of the condition or problemThe Epidemiologic Triad: the relationship between these three factors- Host organism: individual that has or is at risk of cancer- Agent: did they come in contact with some infectious agent?o Can be genetic, composition of the host, infectious agent, or environmental factor- Environment: the place where the environment and the host interactMain Causes of Human Cancer: All interact with each other; main cause multifactorial
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