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PSYC512: Research Methods
Lecture 10
Brian P. Dyre
University of Idaho
PSYC512: Research Methods
Lecture 10 Outline
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Exam Tuesday of Next Week
 Will cover all lecture material, all material in
Howell Chapters 1-5, broad concepts
assumptions from Howell Chapters 6-11
Questions about material covered in Lecture 9
 The Normal Distribution
 Testing Hypotheses
Inferential Statistics
PSYC512: Research Methods
Hypothesis Testing: Inferential
Statistics
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All inferential statistics are evaluating this ratio:
Test statistic =
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Effect (good) Variance
-------------------------------------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
How is the probability of a Type I
error, p, calculated? It depends on…
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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, Chi-square, 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
Four Questions (with subparts) to
Guide Your Choice of Inferential Test
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What are the scaling properties of my measure(s) or dependent
variable(s)?
 How many measures do I have?
 If nominalhow many categories (dichotomous, 2, or nondichotomous, > 2)?
Is/Are my manipulations or independent variable(s) qualitative
(discrete categories) or quantitative?
 If qualitative, how many levels? Note: Often quantitative
variables are manipulated as discrete categories
How many manipulations (factors) do I have?
 Are the factors manipulated independently and exhaustively
(factorial design)?
Are the hypotheses directional or not?
Is effect size (strength of relationship) important to my hypotheses?
PSYC512: Research Methods
Examples?
PSYC512: Research Methods
Next Time…
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The exam!
PSYC512: Research Methods