Chapt.%209

# Essentials of Statistics for the Behavioral Science

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Hypothesis Testing II The t - Distribution

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Assignment 1, 3, 7, 9, 13, 17
Introduction In behavioral research, we often have to estimate the standard deviation of the population from sample data. We assume that the sample data provides a reasonable estimate. However, we are not likely to get extreme scores in our sample. To compensate, we calculate the SD differently when we want to get an estimate of the population standard deviation.

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Comparing Calculations The Standard Deviation for a population: σ = Square root of SS/N The estimated Standard Deviation for a population: s = Square root of SS/n-1
A New Probability Distribution The Unit Normal Distribution is a population distribution. Requires that the population standard deviation is known OR Requires a very accurate estimate of the population standard deviation (n > 45). When we estimate the population standard deviation from small samples we must use the t – distribution rather than the Unit Normal Distribution to find probability.

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## This document was uploaded on 02/18/2011.

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Chapt.%209 - Hypothesis Testing II The t - Distribution...

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