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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Appendix: Behavioral Statistics

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Types of Statistics in Psychology Descriptive Statistics: Summarize numbers so they become more meaningful and easier to communicate to other people Inferential Statistics: Used for making decisions, for generalizing from small samples, and for drawing conclusions

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Graphical Statistics Presenting numbers pictorially (usually in a graph) so they are easier to visualize –Subset of descriptive statistics Frequency Distribution: Table that divides an entire range of scores into a series of equal classes and then records the number of scores that fall into each class

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix More Types of Graphs Histogram: Graph of a frequency distribution; scores are represented by vertical bars Frequency Polygon: Graph where number of scores in each class is represented by points on a line

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Figure A.1

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Figure A.2

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Measures of Central Tendency A number that describes a typical score around which the other scores fall

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Mean Add all the scores for each group and then divide by the total number of scores; one type of average Mean is sensitive to extremely high or low scores in a distribution; not always the best measure of central tendency

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Median Arrange scores from highest to lowest and then select the score that falls in the middle; half the values fall above the median, and half fall below it

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Mode Identifies the most frequently occurring score in a group Easy to obtain but often unreliable Main advantage: Gives the score actually obtained by the most people

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Measures of Variability Provide a single number that tells us how spread out the scores are Range: Difference between the highest and lowest scores Standard Deviation: Index of how much a typical score differs from the mean of a group of scores

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Standard Scores Z Score: Indicates how many standard deviations above or below the mean a score is Normal Curve: Bell-shaped curve, with a large number of scores in the middle and very few extremely high and low scores

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Figure A.3

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Figure A.4

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Inferential Statistics Population: Entire set of subjects, objects, or events of interest (all married students in the United States) –Impossible or impractical to obtain Samples: Smaller cross section of a population –Easier and more practical (and cheaper!) to obtain –More cost effective

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Inferential Statistics (cont.) Sample must be representative –The membership and characteristics of the larger population must be reflected accurately Members of sample must be chosen randomly –Each member of the population must have an equal chance of being selected for the sample

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Statistical Significance Degree to which an event (e.g. results of an experiment, results of a drug trial) is unlikely to have occurred by chance alone

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Correlation Consistent, systematic relationship between two variables, measures, or events Scatter Diagram: Best way to visualize correlation; plots intersection of each pair of measurements as a single point

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Positive Relationship Increases in one measure (X) are matched by increases in the other (Y) –E.g. the more cigarettes you smoke, the more likely you are to contract lung cancer

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Zero Correlation No relationship exists between two variables –E.g. relationship between hair color and intelligence test scores (IQs)

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Negative Relationship (or Correlation) As values of one measure increase (X), values in the other measure decrease (Y) –E.g. the more alcohol you drink, the lower your coordination test scores will be

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Figure A.5

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Coefficient of Correlation Statistical index ranging from –1.00 to +1.00; the sign indicates the direction of the relationship and the number the strength –Perfect Positive Relationship: Correlation of +1.00 –Perfect Negative Relationship: Correlation of –1.00 –Perfect correlations are rarely found in psychology

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Correlation Caution! It is statistically impossible to have a correlation coefficient greater than +1.00 or lesser than –1.00

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Percent of Variance Amount of variation in scores accounted for by the correlation

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Psychology: A Modular Approach to Mind and Behavior, Tenth Edition, Dennis Coon Appendix Utility of Correlations Correlations help us identify relationships that are worth knowing Correlations are valuable for making predictions If a correlation exists, the two variables are related Correlation does NOT demonstrate causation! –Many times a third, or perhaps extraneous, variable could be creating the correlation

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