Chapter 8
Distribution of Differences Between Means
distribution is made up of the difference scores
between randomly selected means population 1 and population 2; only know parameter is the
actual scores in the two samples
Assumption of Independent ttests
•
The test variable is normally distributed for each of the populations
•
The variances of the test variable are equal
•
Cases are a random sample of the population
•
Scores on the test variable are independent
Calculating an Independent ttest
•
Identify populations and null & research hypothesis
•
Identify characteristics of the comparison distribution
o
Estimate population variance for each sample
o
Figure pooled estimate of the estimated population variance
o
Figure variance for distribution of means for each sample
o
Figure variance of the distribution of differences between means
o
Figure standard error
•
Determine
t
critical
•
Determine
t
obtained
•
Accept or Reject Null Hypothesis; Interpret results
Effect Sizes for Independent ttest
difference between the population means divided by the
pooled standard deviation of the population
Chapter 9
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 Fall '07
 Fekete
 Normal Distribution, Standard Deviation, Variance, ANOVAs, Estimate population variance

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