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
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
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
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
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
Procedures for Collecting Data Data Collection Procedures 11 Experiments Direct observation

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Elements of Statistical Studies 12
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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