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Dependent t-Test. CJ 526 Statistical Analysis in Criminal Justice. Overview. Dependent Samples Repeated-Measures. When to Use a Dependent t-Test. Two Dependent Samples Repeated-Measures Design (before-after) Matched-Subjects Design. Example of a Dependent t-Test.

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dependent t test

Dependent t-Test

CJ 526 Statistical Analysis in Criminal Justice

overview
Overview
  • Dependent Samples
      • Repeated-Measures
when to use a dependent t test
When to Use a Dependent t-Test
  • Two Dependent Samples
      • Repeated-Measures Design (before-after)
      • Matched-Subjects Design
example of a dependent t test
Example of a Dependent t-Test
  • A forensic psychologist wants to determine whether physical exercise in a boot camp program has an effect on muscular strength. He/she measures the number of pull-ups 25 program participants complete at the beginning of the program (M = 3.28, SD = 1.88) and at the end of the program (M = 3.6, SD = 1.73).
example of a dependent t test continued
Example of a Dependent t-Test -- continued
  • Number of Samples: 2
  • Nature of Samples: dependent (same subjects at two different points in time)
  •  Known:
example of a dependent t test continued1
Example of a Dependent t-Test -- continued
  • Independent Variable: participation in boot camp--exercise
  • Dependent Variable and its Level of Measurement: number of pull-ups
  • Target Population: boot camp participants
example of a dependent t test continued2
Example of a Dependent t-Test -- continued
  • Appropriate Inferential Statistical Technique: t test, related samples
  • Null Hypothesis: no difference between the groups before and after
  • Alternative Hypothesis: there will be a difference, boot camp participants will be able to do more pullups after training
  • Decision Rule:
      • If the p-value of the obtained test statistic is less than .05, reject the null hypothesis, one-tail test
example of a dependent t test continued3
Example of a Dependent t-Test -- continued
  • Obtained Test Statistic: t
  • Decision: accept or reject null hypothesis
  • D.f. = n-1

(in this case n – 1 = 25 – 1 = 24

results section
Results Section
  • The results of the Dependent t-Test involving participating in a physical exercise program as the independent variable and number of pull-ups as the dependent variable were not statistically significant, t (24) = -1.693.
discussion section
Discussion Section
  • It appears that participating in a physical exercise program does not have an effect on developing muscular strength among participants in a boot camp program.
spss paired samples t test procedure
SPSS Paired-Samples t-Test Procedure
  • Analyze, Compare Means, Paired-Samples t-Test
  • Move pair of variables over to Paired Variables
spss paired samples t test printout
SPSS Paired-Samples t-Test Printout
  • Paired Sample Statistics
    • Paired variables
    • Mean
    • N
    • Standard Deviation
    • Standard Error of the Mean
spss paired samples t test printout continued
SPSS Paired-Samples t-Test Printout -- continued
  • Paired Samples Correlations
    • Paired variables
    • N
    • Correlation
    • Sig
      • p-value of correlation coefficient
spss paired samples t test printout continued1
SPSS Paired-Samples t-Test Printout -- continued
  • Paired Samples Test
    • Paired variables
    • Paired Differences
      • Mean of the Difference
      • Standard Deviation of the Difference
      • Standard Error of the Mean of the Difference
      • 95% Confidence Interval of the Difference
        • Lower
        • Upper
spss paired samples t test printout continued2
SPSS Paired-Samples t-Test Printout -- continued
  • t: obtained test statistic
  • df: degrees of freedom
  • Sig: p-value
    • Divide by 2 to get one-tailed p-value