conf int part 2

# conf int part 2 - Quantitative Methods Z scores and...

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© John M. Ackroff 2008 Quantitative Methods Z scores and Confidence Intervals about  μ, Part II:  The Standard Error of the  Mean and Confidence Intervals February 7, 2008

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© John M. Ackroff 2008 Review The larger the sample, the closer X will  be to μ. If  σ  is relatively small, X will be closer to  μ than if  σ  is relatively large. σ X  =  σ  / √n Standard Error of the Mean
© John M. Ackroff 2008 Sampling Techniques A truly random sample requires that  each member of the population have  the same chance of being chosen each  time a new sample score is drawn. This means that we’re sampling with  replacement. Typically, we sample without replacement. Exit polls Subjects in experiments.

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© John M. Ackroff 2008 Sampling with and without replacement Suppose I have a standard deck of  playing cards.  I select one at random,  note that it’s the 4 of Clubs, and put it  back in the deck.  I then shuffle and  draw another card. What’s the probability it’s a 4? What’s the probability it’s a Club? If I had not put the 4 of Clubs back, what  would these probabilities be?
© John M. Ackroff 2008 What do  σ  and  σ X  tell us? σ  tells us how closely scores are distributed  about μ. σ X  tells us how closely Xs are distributed  about μ. Suppose I draw a sample with n = 1.

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conf int part 2 - Quantitative Methods Z scores and...

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