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Chapter 11
Testing for Differences
Differences betweens groups or categories of the independent variable
Statistical tests of difference reveal whether the differences observed are greater than differences that might occur by chance
Chisquare ttest
ANOVA
Copyright c 2001 The McGrawHill Companies, Inc. 1
Inferential Statistics
Statistical test used to evaluate hypotheses and research questions
Results of the sample assumed to hold true for the population if participants are
Normally distributed on the dependent variable Randomly assigned to categories of the IV
Caveats of application
Copyright c 2001 The McGrawHill Companies, Inc. 2
Alternative and Null Hypotheses
Inferential statistics test the likelihood that the alternative hypothesis is true and the null hypothesis is not
Significance level of .05 is generally the criterion for this decision
If p .05, then alternative hypothesis accepted If p > .05, then null hypothesis is retained
Copyright c 2001 The McGrawHill Companies, Inc. 3
Degrees of Freedom
Represented by df
Specifies how many values vary within a statistical test
Collecting data always carries error df help account for this error
Rules for calculating df or each statistical test
Copyright c 2001 The McGrawHill Companies, Inc. 4
Four Analytical Steps
1. Statistical test determines if a difference exists
2. Examine results to determine if the difference found is the one predicted
3. Is the difference significant?
4. Evaluate the process and procedures of collecting data
Copyright c 2001 The McGrawHill Companies, Inc. 5
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