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This 2 page Class Notes was uploaded by Kayla Ann Berube on Tuesday January 19, 2016. The Class Notes belongs to Stat 110 at a university taught by Wilma Sims in Spring 2016. Since its upload, it has received 7 views.
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Date Created: 01/19/16
Statistics is the science of collecting, classifying, presenting and interpreting data. Where Does Data Come From? • Individuals o The objects described by a set of data. The objects can be people, animals or things. • Variable o Any characteristic of an individual. Variables can take different values for different individuals. Data Sources • Observational Study o Observes individuals and measures variables of interest but does not attempt to influence the responses. o The purpose of an observational study is to describe some group/situation. • Sample Survey o A sample survey is a type of observational study in which a sample is selected and asked to respond to questions. o i.e. public opinion polls, pre-election polls, TV ratings • Experiment o Experiments deliberately impose some treatment on individuals in order to observe their responses. o The purpose of an experiment is to study whether the treatment causes a change in the response. o i.e. In medical studies, patients are given drugs at various dosage levels to study effectiveness. Definitions • Population o The entire group of individuals about which we want information. • Sample o A part of the population from which we actually collect information. o A sample is used to draw conclusions about the population. • Census o A sample survey that attempts to include the entire population in the sample. Key Terms • Individuals and Variable • Population and Sample Collecting Data • We want to select a sample from the population. • We want the objects in the sample to be representative of the population. Samples, Good and Bad • Biased Sampling Design o A design that systematically favors certain outcomes. • Sampling designs that are often biased o Convenience Sampling § Selects whichever individuals are easiest to reach § Interviewer makes the choice o Voluntary Response Sampling § Chooses itself by responding to a general appeal § People make the choice. • Personal choice produces bias. Simple Random Sample (SRS) • Simple Random Sample of size ‘n’ o Consists of ‘n’ individuals from the population chosen in such a way that every set of n individuals has an equal chance to be • A sample is selected using random digits. o Random digits § A long string of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 with these two properties: 1. Each entry is equally likely to be any of the digits 0 – 9 2. The entries are independent of each other. That is, knowledge of one part of the table gives no information about any other part. • Choosing an SRS o Step 1 – Label § Assign a numerical label to every individual in a population. All labels must have the same number of digits. § Labels can be assigned in any manner … i.e. alphabetical order o Step 2 – Table § Use the random number table to select labels at random.
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