Social Science Reasoning Using Statistics

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Social Science Reasoning Using Statistics

• Psychology 138
• Spring 2005

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Performing your statistical test

• What are we doing when we test the hypotheses?
• Consider a variation of our memory experiment
  example

No Memory treatment
Memory patients
Memory treatment
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Performing your statistical test

• What are we doing when we test the hypotheses?
• Consider a variation of our memory experiment
  example

No Memory treatment
Memory patients
Memory treatment
Hypotheses
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Which test do we use?

• The independent sample t-test can be used when

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Testing Hypotheses

• Hypothesis testing a five step program

• Step 1 State your hypotheses
• Step 2 Set your decision criteria
• Step 3 Collect your data
• Step 4 Compute your test statistics
• Compute your estimated standard error
• Compute your t-statistic
• Compute your degrees of freedom
• Step 5 Make a decision about your null hypothesis

These are computed differently than last times
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Performing your statistical test
Independent-samples t
One-sample t
Test statistic
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Performing your statistical test
Independent-samples t
One-sample t
Test statistic
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Performing your statistical test
Independent-samples t
One-sample t
Test statistic

• Population means
• from the hypotheses

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Performing your statistical test
One-sample t
Test statistic
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Performing your statistical test
We combine the variance from the two samples
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Performing your statistical test
We combine the variance from the two samples
Recall weighted means, need to use weighted
variances here
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Performing your statistical test
Independent-samples t

• Compute your estimated standard error

• Compute your t-statistic

• Compute your degrees of freedom

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Performing your statistical test
Need to compute the mean and variability for each
sample
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Performing your statistical test
Need to compute the mean and variability for each
sample
Control group
50
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Performing your statistical test
Need to compute the mean and variability for each
sample
Exp. group
44.5
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Performing your statistical test
0.95
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Performing your statistical test
0.95
Tobs 0.95
Tcrit 2.447
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Performing your statistical test
0.95
Tobs 0.95
Tcrit 2.447
Two-tailed

• 0.05

- Fail to Reject H0
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Performing your statistical test
0.95
Tobs 0.95
Tcrit 2.447
Two-tailed

• 0.05

Compare
Tobs
Tcrit
lt
Fail to reject the H0
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In labs

• Practice hypothesis testing with independent
  samples designs (by hand and using SPSS)