#10 PH150A Feb10 Error Bias

#10 PH150A Feb10 Error Bias - Introdution to Error and Bias...

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Introdution to Error and Bias in Epidemiological Studies PH 150A: Introduction to Epidemiology 2010 2 Objectives • Define inference and validity • How error happens • Contrast random and systematic error and techniques to address • Introduce confounding 3 A Frequent Sequence of Studies in Human Populations Case Studies/Ecological Associations/Case Series Cross Sectional Studies/Surveys Case-Control Studies Cohort Studies Randomized Trials Sometimes referred to as a hierarchy of study designs. 4 Components of analytic epidemiological studies 1. A study question 2. A defined study group 3. Information on study outcome 4. Information on study exposure(s) 5. Assessment of the association between exposure and outcome. 6. Conclusion 5 Conducting a study Research Question Actual Study Study Plan Study Findings Design Implement 6 Why worry about error? • Epidemiological studies attempt to approximate what is going on in the “real world” by evaluating relationship between exposure and outcome in a sample of people • We can never study everyone and we can never measure exposure and outcome perfectly. • Error is inevitable!
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7 Goal:Truth about relationship between exposure and outcome Truth in “real world” Actual people to apply findings (TARGET POPULATION) Actual exposure and outcome Actual relationship between exposure and outcome Approximation in study “Study Group/ Study Population/Study Sample” Measurements collected Results of this study Difference between truth and approximation= error 8 Results of a study are valid when they reflect the truth • Internal validity: refers to the design, methods, analysis and results of an individual study. Did the study do what it intended to do? • External validity refers to whether findings that are internally are also applicable (generalizable) to people other than those included in an individual study. Do the study results apply in the real world? • Inference: process of applying results from a sample to the target population 9 INFERENCE Research Question Actual Study Study Plan Study Findings Truth in Study TRUTH Design Implement Infer Infer ERROR ERROR 10 Where error occurs • Selecting study sample • Measuring exposure and outcome • Interpreting relationship between exposure and outcome 11 Defined Study Group • Target population : complete set of people to whom we want to apply study results • Study Group,Sample, Population = a subset of target population assumed to represent it Process of selecting study group Target population Intended study group Study Population: Actual people in the study
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13 Target population Intended sample Actual study population Exclusions, refusals Inability to perfectly reflect Target population Inability to perfectly reflect intended sample How error influences selecting a study group 14 1807 Mexican
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#10 PH150A Feb10 Error Bias - Introdution to Error and Bias...

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