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# Stats Intro Ps 372

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### Stats Intro Ps 372

1. 1. Statistics: An Introduction Andrew Martin PS 372 Fall 2009
2. 2. We will examine … <ul><li>Methods for describing and exploring data . We will be looking at tables, summary statistics and graphs in order to learn how to extract information from the statistical indicators. </li></ul><ul><li>Statistical inference , or the process of drawing defensible conclusions about populations from samples. </li></ul>
3. 3. How data are organized <ul><li>A data matrix is an array of row and columns that stores the value of data. </li></ul>
4. 4. Data Matrix
5. 5. Data Matrix
6. 6. Data Matrix
7. 7. Remember, four data types <ul><li>Nominal : Variable values are unordered names or labels (Ethnicity, gender, country of origin)‏ </li></ul><ul><li>Ordinal : Variable values are labels having an implicit but unspecified or measured order. Numbers may be assigned to categories to show ordering or ranking, but strictly speaking, mathematical operations are inappropriate. </li></ul><ul><li>(Example: Scale of ideology)‏ </li></ul>
8. 8. Remember, four data types <ul><li>Interval: Numbers are assigned to objects such that interval differences are constant across the scacle, but there is no true or meaningful zero point.(Examples: temperature, intelligence scores)‏ </li></ul><ul><li>Ratio: In addition to having the properties of interval variables, these scales have a meaningful zero value. (Example: income, percentage of the population with a high school education)‏ </li></ul>
9. 10. Frequency Distributions <ul><li>Frequency distributions describe the relative frequencies of each value or a variable. </li></ul><ul><li>Typically, these frequencies are expressed as proportions or percentages of the data. </li></ul>
10. 11. Frequency Distribution
11. 13. Probability <ul><li>Probability is the likelihood that in the long run an observation will have a specific characteristic or an event will occur. </li></ul><ul><ul><li>Probabilities must meet two requirements: </li></ul></ul><ul><ul><li>They must lie between 0 and 1.0 </li></ul></ul><ul><ul><li>For a random process the sum of the probabilities of all the individual outcomes must equal 1.0 </li></ul></ul>
12. 14. Odds <ul><li>Odds refer to the extent or degree to which one response, event or characteristic exceeds another response, event or characteristic. </li></ul><ul><li>Odds are expressed as ratios. </li></ul><ul><li>Ex: 2004 NES question about law prohibiting late-term or partial birth abortions: </li></ul><ul><ul><li>715 favor such as la, 417 oppose it. </li></ul></ul><ul><ul><li>The law is favored by a ratio of 1.7 to 1 </li></ul></ul>