handout02 - HANDOUT#2 TYPES OF STATISTICAL STUDIES TOPICS 1...

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HANDOUT #2 - TYPES OF STATISTICAL STUDIES TOPICS 1. Observational vs Experimental Studies 2. Retrospective vs Prospective Studies 3. Sampling Principles: (a) Probability Sampling: SRS, Systematic, Stratified, Clus- ter (b) Estimation of population parameters 4. Experimental Design Principles 5. Common Problems in Designed Experiments 6. Selecting an Appropriate Design 1
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Sampling From a Population The basic goal of most studies is to use a subset of a population to make a statement about the whole population. These types of situations were illustrated in Handout 1 with our examples of market surveys, polling, estimating ozone levels, determining side-effects of drugs, etc. Two basic types of studies: Observational and Experimental Observational Study : Records information about subjects without applying any treatments to subjects (passive participation of researcher) Examples: Challenger Data, Political Polls, Market Surveys, Industrial Produc- tion Records, Traffic Accident Studies, Epidemiological Studies Experimental Study : Records information about subjects while applying treatments to subjects and controlling study conditions to some degree (active participation of researcher) Examples: Clinical Trials (Some control), Laboratory Studies (More Control), Agricultural Field Trials (Some Control), Greenhouse Experiments (More Con- trol) Observational studies are of four basic types: Sample Survey: Provides information about a population based on a sample from the population at a specific time point. Political Polls, Market Surveys Prospective Study: Observes population in the present by using a sample survey and proceeds to follow the sample forward in time in order to record the occurrence of specific outcomes. Example: Academic success of two groups: Head Start vs No Head Start Retrospective Study: Observes population in the present by using a sample survey and collects information from the sample about the occurrence of specific outcomes that have already taken place. Example: Is incidence of colon cancer related to Diet? Collect information about the diets of two groups of people, those with and those without colon cancer. Epidemiological studies: e. coli outbreak in Europe during summer 2011. 2
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Cross-sectional study: Involves data collected at a specific point in time. This type of study is often used to assess the prevalence of acute or chronic conditions, or to answer questions about the causes of disease or the results of medical intervention. Example: Study the effect of oral contraceptives (OC) on heart disease in women aged 40-44 years. Randomly select 5000 users of OC and 10000 nonusers and record the occurrences or nonoccurrence of myocardial infraction for the 15000 women. Sample Survey Example The Bureau of Labor Statistics determines the unemployment rate. The Current Population Survey (CPS), or ”Household Survey”, conducts a survey based on a sample of 60,000 households.
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