Stats I Final Pitt 2

  1. Paired-sample t-test

    paired-sample t-test
    used to compare 2 means where subjects have been measured twice
  2. examples of when to use a paired-sample t-test

    paired-sample t-test
    • - subject is measured twice on a DV pre and post treatment (aka pre-post design)
    • subject is measured on a DV at different levels of an IV simultaneously (DV = SAT, IV = math, verbal)
    • -subject can be more than one person (DV = happiness, IV = spouses (husband, wife))
  3. Assumptions

    paired-sample t-test
    • Normality
    • No Outliers
    • Independence of subjects
  4. Assumptions: Normality

    paired-sample t-test
    • the difference score of a DV (error term) should be normally distributed
    • tested using Shapiro-Wilk
  5. Assumption: when Normality is violated

    paired-sample t-test
    • a research question can still be answered by using an alternative test that does NOT assume normality
    • a non-parametric alternative to the paired-sample t-test is Wilcoxon signed rank test
  6. Assumption: Outliers

    paired-sample t-test
    • has an undue influence on a statistic
    • assumption is checked by examining histogram and Q-Q plot
  7. Assumption: Independence of Subjects

    paired-sample t-test
    • design considerdation
    • one subject score is not influenced by another subject in study
    • cannot be tested using statistics
  8. Degrees of Freedom

    paired-sample t-test
    df= N-1

    doesn't depend on the number of scores but rather on the number of subjects
  9. Confidence Interval

    paired-sample t-test
    • interval estimation
    • accounts for uncertainty of error
  10. Disadvantages

    paired-sample t-test
    Order effect

    Carryover effects

    Test effects
  11. Disadvantages: Order effect

    paired-sample t-test
    • when the outcome of the study is affected by the order in which the treatments were prepared.
    • Two most common types: carryover and test effects
  12. Order effect: Carryover effects

    paired-sample t-test
    effects of one treatment do not end prior to the administration of another treatment, so the effects observed in the later treatment include residual effects of the former

    ex: testing new pill but not waiting long enough between dosages
  13. Order effect: Testing Effect

    paired-sample t-test
    fatigue and practice effects

    effects due to repeated testing of participants over time

    ex: taking the same test twice in a short period of time
  14. Counterbalancing

    paired-sample t-test
    common solution to an order effect

    the order of treatments is often counterbalanced so that some participants get treatment in order but other get a second order so that order effects can be assessed.
  15. Advantages

    paired-sample t-test
    Reduced error: variance within subjects is typically smaller than between subjects (smaller sampling error, more power)

    Number of subjects: paired-samples t-test requires smaller number of subjects to achieve the same power than the independent-samples t-test
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Stats I Final Pitt 2
Stats I Final Pitt pt. 2