Lecture 8 Cancer Epidemiology 1775 Percival Potts was the first to see a link between the Chimney sweeps coal tar and a particular type of cancer adenocarcinoma This particular population was at risk for cancer What is Epidemiology It s the study of patterns causes and effects of health and disease in defined populations Looks for causes and risk factors of disease in order to propose effective strategies for disease prevention and control The epidemiological approach This approach attempts to Gather epidemiological evidence Form a hypothesis Test hypothesis statistics support hypothesis make recommendations for changes that will protect the public stats do not support either revise hypothesis or not Multiple analysis may generate conflicting reports distrust and skepticism Determine if an observed difference is a real difference if it is tried to determine why there is a difference How do we evaluate evidence P value a statistical test estimates probability that an observed difference would appear by chance even if no difference really exists calculating a p value will tell us if a real difference in the rate of cancer development exists or if it just looks like it does really just random Statistical significance likelihood that observed difference is real Bias can cause conflicting results Some possible reasons Experimenter bias Detection bias Selection bias Recall bias Publication bias The effect of bias Experimenter preconceptions influence results Detection methods are unequal Recall self reporting errors Selection nonrandom volunteering Publication relationship publish no relationship no publish 20 stories 19 show no relationship while 1 shows the misleading story is the one published If the p value is 0 05 then 5 of the time we are misled Epidemiologic data is age adjusted age is a confounding factor and must be accounted for in comparisons of groups Types of epidemiology Observational is like the cleantown vs chemtown example testing one particular factor Experimental human equivalent of animal testing providing or withholding a substance to determine its toxic or beneficial effects greatly 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 population attempts to find correlations among characteristics such as diet air quality occupation comparisons are frequently made between countries and smaller geographic regions attempts to uncover and portray the occurrence of the condition or problem Epidemiological studies The most common types are observational studies case control studies and cohort studies Experimental studies randomized control trial done to test a preventive or therapeutic regimen to diagnostic procedure Aims to remove the effects of unknown sources of bias Limitations of epidemiology Epidemiological studies can never prove causation it cannot prove that a specific risk factor actually causes the disease being studied Epidemiological evidence can only show that a risk factor is associated correlated with a higher incidence of disease in the population The strength of an epidemiological study depends on the number of cases and controls included in the study p value gets smaller relationship less likely due to chance The epidemiologic triad Host organism in cancer it is the person or human Agent can be genetic composition of the host infectious agent or environmental factor Environment place in which the agents and host interact Main causes of human cancer at 60 your risk is 1000x greater than at 40 radiation viral exposure chemicals tobacco use diet alcohol consumption Age Hereditary Environment Lifestyle what do you get from your parents and grandparents Case control study What is risk Use patients who already have a disease or other condition and see if there are characteristics of these patients that differ from those who don t have the disease Epidemiological risk refers to a probability chance that something may occur but not guaranteed Determined by studying large groups of people to discover the probability that any given person will develop the disease over a certain period of time Two categories of risk absolute and relative Absolute numeric chance probability of developing cancer during a specified time period Relative gives you comparison or ration rather than an absolute value Interpreting risk When reading about cancer risk statistics you have to pay attention to details like Who s being observed ages genetic predisposition and geography How many people were studied Studies with larger of ppl are more accurate than Have similar studies been done The findings of one study are more reliable if they re studies that examine a small group similar to findings by other studies Incidence Mortality Incidence of disease rate at which new cases occur in a population during a specified period Mortality of cancer related deaths during specific time period The incidence and mortality rate describe of new cases deaths from cancer per 100 000 people during specific time period usually 1 year Cancer prevalence the number percent of living people who have ever been diagnosed with cancer Includes how often cancer occurs incidence and by how long people live after diagnosis survival Prevalence rates express of cases of cancer per 100 000 people Prevalence
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