Lecture2_Stat104v12_1up

Lecture2_Stat104v12_1up - Stat 104: Quantitative Methods...

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Stat 104: Quantitative Methods for Economists Class 2: Getting (good?) Data 1
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One of many definitions… s Statistics is a collection of procedures and principles for gathering data and analyzing information in order to help people make decisions when faced with uncertainty. s In statistics, the questions we have are about a population. 2
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Population s The population is the entire collection of objects or individuals about which information is desired. s Ex: If we want to determine the % of men on this campus, the population is ALL the people on this campus. s Ex: If we want to determine the percentage of men in the US, the population is ALL people in the US. 3
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Can we obtain the population? s For the college example, the university probably has the exact list of students on this campus so yes, the population can be obtained. s But, for the US, there is not a list of all the people. And what about tourists, etc. . Who exactly makes up your population? 4
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Sampling If we can’t obtain the population, we’ll look obtain a sample to obtain a sample which is a subset of the population. Population Sample 5
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Good properties of a sample s What properties would you like the sample to have? 1. 2. 3. 6
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From sample to population Statistics: the science of collecting, presenting, analyzing and interpreting data to assist in making effective decisions. s Descriptive statistics b Collecting, presenting, and describing data s Inferential statistics b Drawing conclusions and/or making decisions concerning a population based only on sample data 7
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Descriptive Statistics s Collect data b e.g., Survey, Observation, Experiments s Present data b e.g., Charts and graphs s Characterize (describe) data b e.g., Sample mean 8
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Inferential Statistics s Estimation b e.g., Estimate the population ean weight using the sample Drawing conclusions and/or making decisions concerning a population based on sample results. mean weight using the sample mean weight s Hypothesis Testing b e.g., Use sample evidence to test the claim that the population mean weight is 120 pounds 9
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Important Warning s Statistical studies are driven by data. s How we collect data is at least as important as ow we analyze it. how we analyze it. s In particular, a sample should be representative of the population, and random sampling (everyone in the population is equally likely to be selected), is often the best way to achieve this. 10
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Procedures for Collecting Data Data Collection Procedures 11 Experiments Direct observation
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Elements of Statistical Studies 12
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Observational Study s Observational study : Record data on individuals without attempting to influence the responses. We typically cannot effect this way. s
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This note was uploaded on 03/27/2012 for the course STATS 104 taught by Professor Michaelparzen during the Fall '11 term at Harvard.

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Lecture2_Stat104v12_1up - Stat 104: Quantitative Methods...

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