Exam 3 Study Guide
Exam 3 Study Guide POS 3713
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This 3 page Study Guide was uploaded by Leah Burkett on Monday May 2, 2016. The Study Guide belongs to POS 3713 at Florida State University taught by Dr. Matthew Pietryka in Spring 2016. Since its upload, it has received 27 views. For similar materials see Political Science Research Methods in Political Science at Florida State University.
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Date Created: 05/02/16
Political Science Study Guide: Exam III 1. What is the difference between a sample and a population and why do we care about each? Population: is data for every possible relevant case Sample: subset of cases that are drawn from an underlying population. We are interested in the sample only so far as it helps us to learn about the underlying population. 2. What is a normal distribution and what information can we learn from its mean and Standard deviation? A normal distribution is “bell-shaped”. 1) Systemetrical about its mean 2) Predictable area under the curve 68-95-99.7 3. What is the central limit theorem? How does it allow us to calculate the uncertainty of our estimates of population parameters? The central limit theorem. 1) Take random sample Sample means should 2) Calculate sample mean be 3) Take new sample Normally distributed. 4) Calculate sample mean 5) Repeat steps 1-4 an infinite # of times 6) Plot sample means 4. What is a Random Sample and how does it differ from a convenience sample? Why does Central Limit Theorem only apply to random samples? Random Sample: every case in your population of interest has an equal chance of being selected as part of the sample. The Central Limit Theorem only applies to random samples because the more we randomly select from the population, the distribution of sample means become more normally distributed. 5. How do you interpret a 95% confidence interval? 95% of the area under a normal curve lies within two standard deviations from the mean. 6. How does sample size affect the standard error of the mean? Standard Error of the Mean:σ= Sy/√n Larger sample sizes will reduce the size of the standard errors. Smaller samples sizes will increase the standard error. 7. What is a p-value? Be sure to understand what it tells you and as well as what it does not tell you? P-value: ranges between 1 and 0; probability that we would see the relationship that we are finding because of random chance. The probability that we would see the observed relationship between the two variables in our sample data if there were truly no relationship between them in the unobserved population. 8. What is the Null Hypothesis and how does it relate to the p-value? What is the alternative hypothesis? Null Hypothesis: a theory based statement but ut is about what we would expect to observe if our theory was incorrect. Alternative hypothesis: is if the statement is true, the p-value conveys the level of confidence with which we can reject the Null hypothesis. 9. What is the difference between one and two-tailed tests and how do we choose the appropriate one? Two-tailed tests- Ho: β=O One-tailed tests- Ho: β≤0 Ha: ≠ 0 Ha: β>0 In a two-tailed test you are testing if the mean is significantly greater than X AND of the mean is significantly less than X. While in a one-tailed test you are only testing if the mean is significantly greater than OR less than X. 10. What is statistically significance? What does it mean if a relationship is not statistically significant? Statistical Significance: is achieved only to the extent that the assumptions underlying the calculation of the p-value had. P is less than .05 it is statistically significant. 11. What are the bivariate hypothesis tests and how do we determine which one is the most appropriate to test given Hypothesis? Tabular Analysis: Both things being tested are categorical Difference of Means: if one thing being tested is categorical and the other is continuous Correlation Coefficient: Both things being tested are continuous 12. What is the Difference between categorical, ordinal, and continuous variables? Categorical: difference in values represent difference in kind NOT value Ordinal: Difference in Rank between units Continuous: meaningful order, Equal unit differences. 13. How do you interpret a correlation coefficient? +1 -1 0 14. How do you assess a relationship in a tabular analysis? You use a X^2 formula to find the strength of each relationship. Compare value to critical value. 15. What does a difference of means tell us? What would we expect if there was NO relationship 16. Know how to calculate and interpret: a. The standard Error of the mean – σy=Sy/√n b. Margin of Error- Z= σ/√n c. 95% confidence Interval d. a X^2 - X^2 =∑ (O-E)^2/E e. Difference of means- t= y-y/SE
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