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Unformatted text preview: Sampling distributions and Standard error Chapters 9 & 11 2 Sample vs. Population • Focus will now shift to sample means , rather than individual scores. • Population : • Complete set of individuals, objects, or scores that the investigator is interested in studying. • In an actual experiment, the population is the larger group of individuals from which the experimental subjects have been taken. • The group that you want to draw inferences about. • Sample : • A subset of the population from which the experimental data is collected. 3 Examples of Samples and Population 4 Why Study Samples? • Often not practical to study an entire population. • Instead, researchers attempt to make samples representative of the populations. – Random Selection: • Each member of the population has an equal chance of being sampled. • Good but difficult. – Haphazard Selection: • Take steps to ensure samples do not differ from the population in systematic ways. • Not as good but much more practical. 5 Population and Sample • General strategy in Psychology: – Study a group of individuals who are believed to be representative of the general population (or some particular population of interest) • A “parameter” is a characteristic of a population. – Example : the average heart rate of all Canadians. • A “statistic” is a characteristic of a sample. – Example : the average heart rate of a sample of Canadians • We use statistics of samples to estimate parameters of populations. 6 Statistics and Parameters • Statistic b estimates b parameter Population M (or μ) Population SD Population SD 2 ρ “rho” M SD SD 2 r 7 Random Sampling Model • Takes into account chance factors (sampling variation) when sample results are being interpreted. • A common problem in statistical inference involves making inferences about population mean from M. • A random sample is a sample drawn from a population such that each possible sample of the specified size has an equal probability of being selected. – Telephone or housetohouse interviews conducted only in the evening, which automatically eliminates people who hold night jobs....
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This note was uploaded on 04/29/2010 for the course PSYCH 315 taught by Professor Afroditipanagopoulos during the Winter '10 term at Concordia Canada.
 Winter '10
 AfroditiPanagopoulos

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