MicroBio 160 1st Edition Lecture 9 Outline 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 Angiogenesis VII Tumors need Blood Vessels to Grow VIII Cancer Cells Produce Angiogenesis Stimulating Molecules IX Treating Cancer by Inhibition of Angiogenesis X Tumor Angiogenesis Outline of Current Lecture I What is Epidemiology II The Epidemiological Approach III Epidemiological Study IV How do we Evaluate Evidence V Comparison of Disease in Different Locations VI What s the Difference VII The Effect of Bias VIII Limitations of Epidemiology IX Types of Epidemiology X The Epidemiologic Triad XI Main Causes of Cancer Current Lecture What 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 populations o 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 difference o Gather Evidence o Form a hypothesis o 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 skepticism An Epidemiological Study Observations Pollution from chemical factory makes Chemtown stink 100 cases of bladder cancer in Cleantown 200 cases of bladder cancer in Chemtown Hypothesis Chemical pollutants in the air cause people to develop bladder cancer at a higher rate in Chemtown How to Evaluate Evidence After you run all statistical test what are the chances there is a link P value is a statistical test o Estimates the probability that an observed difference would appear by chance even if no difference exists o 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 significance o Likelihood that observed difference is real P value 05 means 5 chance difference is false and a 95 chance that difference is real Cancer 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 to determine if the difference is statistically significant this generates a p value Research Group 1 Hypothesize that living in Chemtown does put one at a significantly higher risk of developing bladder cancer Research Group 2 Hypothesize that living in Chemtown does not put one at a significantly higher risk of developing bladder cancer Their 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 minimum acceptable p value for significance at 05 a fairly stringent level Yes because their calculated p value is LOWER than 05 No because their calculated p value is HIGHER than 05 They 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 publish o No relationship no publish o 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 studied o Evidence can only show that a risk factor is associated with a higher incidence of disease in the population o 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 value Types of Epidemiology Observational Cleantown vs Chemtown Experimental human equivalent of animal testing providing or withholding a substance to determine its toxic or beneficial effects o 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 populations o Attempts to find correlations among characteristics such as diet air quality and occupation o Comparisons are frequently made between countries and smaller geographic regions o Attempts to uncover and portray the occurrence of the condition or problem The 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 interact Main Causes of Human Cancer All interact with each other main cause multifactorial origins multiple causes Age at 60 your risk is 1000 times greater than at 40 Environment radiation viral exposure chemicals Lifestyle
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