12 - Intro to Statistical Inference

12 - Intro to Statistical Inference - Chapter 12:...

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Unformatted text preview: Chapter 12: Introduction to Statistical Inference • Statistical Inference (drawing conclusion about population parameter from sample statistic) • Variety of research questions can ask about a single mean – Is mean of group different from a certain value? – Is mean higher (lower) than certain value? – Is mean between two values? • Start with hypothesis (e.g., population mean equals certain value) • What sample means would occur IF the hypothesis is TRUE • Obtain a random sample and compare mean with sampling distribution of the mean General Procedure for Hypothesis Testing • Step 1: Develop H and H A • Step 2: Find Mean of random sample • Step 3: Examine Sampling Distribution of Mean (values likely if H is true) • Step 4: Retain H if sample result is not sufficiently unlikely (by chance) to reject H Research Question • A developmental psychologist is interested in when young children acquire their first words. She knows that the national average age of first word utterances is 13 months, with a standard deviation of 2.75 months. She takes a random sample of 25 young children from her region to see how it compares to the average. Null and Alternative Hypothesis • Test the question in terms of Null and Alternative Hypotheses • Null ( H ) -- hypothesis researcher puts to the test – E.g., µ X = value • Alternative ( H A ) – contradictory hypothesis (usually hypothesis researcher wishes to support; e.g., µ X ≠ value) • Both H and H A are statements about population parameter • Decision is to reject or retain H • Reject H when observed mean is sufficiently unlikely to have occurred by chance if H is true Directional vs. Nondirectional Hypotheses • H A can be either directional or nondirectional • Nondirectional : Population parameter may be greater than or less than the value stated in H – Also known as a two-tailed test • Directional...
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This note was uploaded on 04/17/2008 for the course PSY 201 taught by Professor Arthur during the Spring '08 term at Purdue University.

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12 - Intro to Statistical Inference - Chapter 12:...

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