EPI 390 Lecture 7Outline of Last Lecture I. Populations in Epidemiologya. “Caseness”II. Review of Prevalence vs. IncidenceIII. Interpreting Odds Ratio/Risk Ratio and Relative RiskIV. Case Study: Chili PeppersV. Case Study: Colon cancer and meat consumptionOutline of Current Lecture I. Epidemiological MeasuresII. Sample Stratification Contingency TablesIII. Continuation of the Chili Pepper Case StudyIV. Relaying Information in your StudyV. Introduction to OsteoporosisCurrent LectureI. Epidemiological Measuresa. Retrospective studies are done on data that is already collected and has been generated without necessarily having a hypothesis in mind.i. Researchers go back and reanalyze data in light of a newly generated hypothesis in order to see if new patterns arise.ii. NHANES – a database of descriptive data that the general public has access to. 1. Collects national health data.II. Sample Stratification and Contingency Tablesa. Sample Stratificationi. Stratified sampling divides a heterogeneous sample population into homogeneous subgroups in order to ensure that at least one observation is drawn from each strata and the risk of excluding important data is minimalized.1. It can be used to measure proportions of the sample population exhibiting a certain classificationb. Sample stratification is interpreted statistically with means and proportions, via contingency tables.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.i. Contingency table: (exposure plus = high risk), (consumer-less = exposure minus)ii. Stratified by controls (i.e. age and sex)1. These controls are dichotomized c. Can’t preclude people with disease because you’re not asking them the right questionsIII. Continuation of the Chili Pepper Case Studya. Consumers (not the controls), aka the exposed individuals were 5.5 (point estimate) times more likely (more, because on pos. side of one) to have gastric cancer compared to controls (non exposed group)i. This shows eating chili peppers is not protective of gastric cancerii. Association vs. Causality – this is association.b. Can’t see if it’s “more significant” based on how small p-value is. The way to make it “more” significant is to choose a smaller p-value. i.e. .01 instead of .05; you’re likely to be wrong 1 out of a 100 times vs. 5 out of 100c. Arbitrary stratification (i.e. how hot do you like your food) – have to be able to interpret with caution because it depends on self-identification.IV.RelayingInformation in your Studya. You don’t get hired for what you learn, but what you do. It is important to be able to design a study, and analyze and relay your data.i. To make sure your results are sound, you need to be able to replicate your studyb. Criteria for designing/evaluating a studyi. Go evaluate your results in the environment/public/(scientific) communityii. Announce suggested association. It should have a benefit to public healthiii. Exploratory analysisiv. Replicate it/see what others have donev. Hypothesis has to be potentially falsifiableCancerChili pepper consumptionYes No TotalYes 204 552 756No 9 145 154Total 213 697 910vi. The “what can you do” is can you design a study to replicate/support observations?vii. You have to be careful of confounding the relationship1. i.e. rate, frequency, quantity, durationviii. There are websites to help control for all covariates out there: i.e. cdc.govc. Goals in epidemiological experiments –i. Find big issue in public health, find span/scope/resources needed/etc. in terms of populations1. Case list: What portions of population do you have to target?ii. Have to understand the scientific problem1. i.e. with osteoporosis: you need to know how bones grow/break/when can you no longer effect change in bones/inevitability)2. You want equilibrium. You don’t want leaking out from bone reservoir or too little minerals stored.V. Introduction to Osteoporosisa. Cost-benefit of (not) drinking milk – i.e. bone health/osteoporosis vs. vascular diseasei. Thresholds to protection and disease1. What’s in milk that you need? Other sources of those components? 0% association between milk and bone health.ii. Components in milk (that you can get elsewhere) that you absolutely need to survive, i.e. calcium.b. Risk of Osteoporosisi. Risk Factors – Osteoporosis results in bone fragility and fractureii. Those at risk include:1. Early menopausal and post menopausal women2. Individuals with low physical activity3. Aged men4. Individuals with low dietary calcium intake5. Young women with prolonged lactation6. Limited sunlight exposure7. Cigarette smokers8. Individuals with genetic predispositionc. Working definition of Osteoporosis – a skeletal disease characterized by low bonemass and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to