Lecture+6+SU10+_sampling+error_

Lecture+6+SU10+_sampling+error_ - Sociology 210 Lecture 6...

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02/23/11 Soc 210 summer 2010 1 Sociology 210 Lecture 6: Sampling Error and Sampling Distributions

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02/23/11 Soc 210 summer 2010 2 Steps for Solving Standardized Normal Distribution Problems Compute Z-scores for the value(s) of interest (unless problem provides this information). Draw a quick diagram, with mean, value of interest and shade area under the curve that you need to find. Find the size (proportion) of the area you shaded in the diagram using Unit Normal Table, your drawing, and knowledge about normal distribution (symmetric, total area under the curve = 1). If the problem is a “story” problem, be sure to state the answer to the question in words, referring to the variables in the problem (i.e. 68.42% of respondents scored between 12 and 22 on the exam).
02/23/11 Soc 210 summer 2010 3 Review: Using Standardized Normal Distribution to Determine Probabilities

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02/23/11 Soc 210 summer 2010 4 Review: Unit Normal Table
02/23/11 Soc 210 summer 2010 5 Example Assume years of employment within a company is distributed normally in the population with mean = 13 and standard deviation = 3. What is the probability that a randomly chosen individual will have at least 14 years of employment? Calculate the Z score: (14-13)/3 = 0.333 Draw Diagram Look up P(Z > 0.333) in Column C of Unit Normal Table. We want Column C because it tells us the probability of that Z-score or higher. The p-value (probability) of having at least 14 years of employment is .3707. About 37% of the employees have logged at least 14 years of service.

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02/23/11 Soc 210 summer 2010 6 Exercise Assume that test scores for a class are
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Lecture+6+SU10+_sampling+error_ - Sociology 210 Lecture 6...

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