Stats I Final Pitt 2

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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

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.