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PSYC512: Research Methods Lecture 9

PSYC512: Research Methods Lecture 9. Brian P. Dyre University of Idaho. Lecture 8 Outline. Exam Next Week Will cover all lecture material, all material in Howell Chapters 1-5, broad concepts assumptions from Howell Chapters 6-11 What do I mean by “broad concepts?”

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PSYC512: Research Methods Lecture 9

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  1. PSYC512: Research MethodsLecture 9 Brian P. Dyre University of Idaho PSYC512: Research Methods

  2. Lecture 8 Outline • Exam Next Week • Will cover all lecture material, all material in Howell Chapters 1-5, broad concepts assumptions from Howell Chapters 6-11 • What do I mean by “broad concepts?” • which tests are associated with which types of scaling properties of variables? • What variants of the tests exist and why? • What assumptions underlie the test? • Questions about material covered in Lecture 8 • Describing Data • The Normal Distribution • Testing Hypotheses • Inferential Statistics PSYC512: Research Methods

  3. Review: The Normal Distribution • What is the difference between a normal distribution and a standard normal distribution? • What is the difference between a raw score and a standardized score? • What are confidence intervals? PSYC512: Research Methods

  4. Testing Hypotheses • Hypothesis testing is the process by which hypothetical relationships between intervening variables are assessed • Hypotheses are always tested relative to one-another or to a “null” hypothesis • Examples • Comparing groups • Assessing performance interventions • Assessing relationships between variables PSYC512: Research Methods

  5. Null-Hypothesis Testing and Inferential Statistics • 2 possible realities • Relationship between your variables does not exist—a null relationship (Ho, the null hypothesis) • Relationship between the two variables in question actually exists (H1, the experimental or alternative hypothesis) • 2 possible decisions when looking at the data • Conclude that a relationship exists (reject the null hypothesis, Ho  DISCONFIRMATION!) • Conclude that no relationship exists (do not reject the null hypothesis  CONFIRMATION? NO!) PSYC512: Research Methods

  6. Null-Hypothesis Testing and Inferential Statistics True State of the World 2 realities by 2 decisions form a 2 x 2 matrix of 4 possibilites Decision PSYC512: Research Methods

  7. Null-Hypothesis Testing and Inferential Statistics 1 Population • Why might we observe a difference between two groups if no difference actually exists (null is true; samples are drawn from the same population)? • Each sample may have a unique mean due to sampling error Frequency m 2 samples Frequency PSYC512: Research Methods

  8. Null-Hypothesis Testing and Inferential Statistics 2 Populations • How does this change if a difference actually exists between my groups? • Each sample has a unique mean that represents both sampling error and the differences between the 2 populations Frequency m1 m2 Frequency PSYC512: Research Methods

  9. Hypothesis Testing: Probability and Statistics • Problem: How do we distinguish real differences or relationships from measurement noise? • Probability and statistics may be used to assess (descriptive statistics) or compare (inferential statistics) the relative magnitude of different types of variability • Effect (treatment) Variance • Variability due to relationship between variables or effect of different levels of independent variable (treatments) • “Good” variance that we want to maximize • Error Variance • Variability in measure due to factors other than the treatment • “Bad” variance that we want to minimize PSYC512: Research Methods

  10. Hypothesis Testing: Inferential Statistics • All inferential statistics are evaluating this ratio: Effect (good) Variance Test statistic = -------------------------------------- Error (bad) Variance • Example test statistics: Chi-square, t, F • These test statistics have known distributions that then allow us to estimate p, the probability of a Type I error (inappropriately rejecting the null hypothesis) • Decision to reject null is made by comparing p to some generally accepted criterion for Type I error probability, a = .05 PSYC512: Research Methods

  11. How is the probability of a Type I error, p, calculated? It depends on… • Scaling properties of your dependent variable (DV) • DV is interval or ratio parametric tests • DV is nominal or ordinal non-parametric tests • Research design • Experimental – test differences on measure between conditions or groups  t-test, ANOVA, sign test, Mann-Whitney • Correlational – test relations between different measures  Pearson product-moment correlation, point-biserial correlation, etc. • Manner in which you phrase your hypotheses • One tailed vs. two-tailed tests PSYC512: Research Methods

  12. Examples? PSYC512: Research Methods

  13. Next Time… • Topic: Review of broad concepts related to power, Chi-square, t-tests, and correlation • Be sure to: • Review Howell chapters 6-10 • Bring questions! • Continue searching and reading the scientific literature for your proposal PSYC512: Research Methods

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