mid-term2fall07answer key

mid-term2fall07answer key - POLS 203 MID-TERM 2 FALL 2007...

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POLS 203 MID-TERM 2 FALL 2007 The multiple choice questions are 3 points each. Please circle one correct answer, if more than one answer is selected, the question will be graded 0 point. The short answer questions are 5 to 10 points each. For these questions, please write all the steps in arriving at the answer. An answer that would only report the end result will receive a 0 point. 1. In comparing a sampling distribution with a population distribution, a. there will always be more variance in the sampling distribution b. there will always be more variance in the population distribution c. as the size of the sample increases the two distributions will become identical d. the two distributions will always be the same 2. In a t test of differences between means, increasing sample size will affect a. degrees of freedom b. standard deviation of the sampling distribution c. t score d. all of the above e. a and b only 3. What is the term for sampling distribution’s standard deviation? How would you explain this concept to a lay person (i.e. who has not studied statistics)? (5 points) It is called “standard error”. I would explain this concept as follows: Imagine we selected many  random samples of same size from a population. We take their means and look at how these means  are distributed. Some of these samples’ means will be below the actual population mean, some will be  above. This distribution of all possible random samples’ means is called the sampling distribution. If  the samples are at least 100 or more in size, the mean of this sampling distribution will be equal to  the population mean. This implies, then, that the standard error shows the average amount of  dispersion around the population (and thus the sampling distribution’s) mean. If we are trying to  predict the population’s mean, by looking at the amount of dispersion in the sampling distribution,  we can know how far any sample’s mean might be away from it (hence, the name “standard error”) . 4. If a normal population has μ=50 and σ=10, what is the mean and standard deviation of the sampling distribution of the mean, based on a sample size n=16? a. μ=50, σ x =2.5 b. μ=3.1, σ x =0.6 c. μ=5, σ x =1.6 d. μ=50, σ x =2 5. Rejection of the null hypothesis in the two-sample case implies that the a. samples are different on the variable of interest b. populations from which the samples are drawn are not same on the variable of interest c. samples are not different on the variable of interest d. populations from which the samples are drawn are identical
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6. Which assumption must be true in order to justify the use of hypothesis testing? a.
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mid-term2fall07answer key - POLS 203 MID-TERM 2 FALL 2007...

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